Microhard Systems MHX-2400 User manual

Operating Manual
MHX-2400
2.4 GHz Spread Spectrum OEM Transceiver
Revision 1.11, December 1, 2000
Microhard Systems Inc.
#110, 1144 - 29th Ave. N.E.
Calgary, Alberta T2E 7P1
Phone: [phone]
Fax: [phone]
www.microhardcorp.com

ii MHX-2400 Operating Manual
MHX-2400
2.4 GHz
Spread-Spectrum
Embedded Modem
WARNING
In order to comply with the FCC/IC
adopted RF exposure requirements, this
transmitter system will be installed by the
manufacturer's reseller professional.
Installation of all antennas must be
performed in a manner that will provide at
least 20 cm clearance from the front
radiating aperture, to any user or member
of the public.
This manual contains information of proprietary interest to
Microhard Systems Inc. It has been supplied in confidence to
purchasers and users of the MHX-2400, and by accepting this
material the recipient agrees that the contents will not be copied
or reproduced, in whole or in part, without prior written consent
of Microhard Systems Inc.
Microhard Systems Inc. has made every effort to assure that this
document is accurate and complete. However, the company
reserves the right to make changes or enhancements to the
manual and/or the product described herein at any time and
without notice. Furthermore, Microhard Systems Inc. assumes
no liability resulting from any omissions in this document, or
out of the application or use of the device described herein.
Microhard Systems’ products are appropriate for home, office,
or industrial use, but are not authorized for utilization in
applications where failure could result in damage to property or
human injury or loss of life.
The electronic equipment described in this manual generates,
uses, and radiates radio frequency energy. Operation of this
equipment in a residential area may cause radio interference, in
which case the user, at his own expense, will be required to take
whatever measures necessary to correct the interference.
FCC Declaration of Conformity
This device complies with Part 15 of the FCC Rules.
Operation is subject to the following two conditions: (1) this
device may not cause harmful interference, and (2) this
device must accept any interference received including
interference that may caused undesired operation.
Microhard Systems Inc.’s products are warranted against all
failures which occur as a result of defective material or
workmanship within 12 months of purchase by the user. This
warranty does not extend to products that, in the opinion of
Microhard Systems Inc., have been subject to misuse, accidents,
lightning strikes, improper installation or application, nor shall
it extend to units which have, in Microhard Systems Inc.’s
opinion, been opened, tampered with or repaired by an
unauthorized facility.
Microhard Systems Inc.
Leaders in Wireless Telecom
#110, 1144 - 29th Ave. N.E.
Calgary, Alberta T2E 7P1
Phone: [phone]
Fax: [phone]
www.microhardcorp.com
© 2000 by Microhard Systems Inc., All Rights Reserved.
HyperTerminal is copyrighted by Hilgraeve Inc, and developed for Microsoft.
Microsoft and Windows are registered trademarks of Microsoft Corporation.
pcANYWHERE and Symantec are registered trademarks of Symantec Corp.
All other products mentioned in this document are trademarks or registered
trademarks of their respective holders.
Manual Revision 1.11, December 1, 2000.

Contents
1. Introduction
1.0 Product Overview .............................................................................................................................................................................. 1
1.1 Features.............................................................................................................................................................................................. 1
1.2 About this Manual............................................................................................................................................................................. 2
2. Initial Setup and Configuration
2.0 Unpacking and Inspection ................................................................................................................................................................. 3
2.1 Additional Requirements................................................................................................................................................................... 3
2.2 Connectors and Indicators.................................................................................................................................................................. 3
2.3 Configuration..................................................................................................................................................................................... 6
2.4 Checking the Link............................................................................................................................................................................... 6
3. Configuration Options
3.0 Command Line Interface.................................................................................................................................................................... 9
3.1 AT Commands................................................................................................................................................................................. 10
A - Answer........................................................................................................................................................................................ 10
E - Command Echo.......................................................................................................................................................................... 10
I - Identification ............................................................................................................................................................................... 10
O - Online Mode.............................................................................................................................................................................. 11
Q - Quiet Mode................................................................................................................................................................................ 11
V - Result Codes Display................................................................................................................................................................. 11
W - Connection Result..................................................................................................................................................................... 11
Z - Reset Modem and load stored configuration.............................................................................................................................. 11
&C - DCD (Data Carrier Detect) ..................................................................................................................................................... 11
&D - DTR (Data Terminal Ready)................................................................................................................................................... 11
&F - Load Factory default configuration ......................................................................................................................................... 12
&K - Handshaking............................................................................................................................................................................ 12
&S - DSR (Data Set Ready)............................................................................................................................................................. 12
&V - View Configuration ................................................................................................................................................................. 12
&E - Framing Error Check................................................................................................................................................................ 12
&W - Write Configuration to memory............................................................................................................................................. 12
Sxxx? - Read S register value........................................................................................................................................................... 12
Sxxx=yyy - Set S register value ....................................................................................................................................................... 12
3.2 Command Result Codes................................................................................................................................................................... 13
3.3 S Registers....................................................................................................................................................................................... 14
S Register 2 - Escape Code............................................................................................................................................................... 14
S Register 3 - CR Control Code....................................................................................................................................................... 14
S Register 4 - Linefeed Control Code .............................................................................................................................................. 14
S Register 5 - Backspace Control Code........................................................................................................................................... 14
S Register 101 - Operating Mode..................................................................................................................................................... 15
S Register 102 - Serial Baud Rate.................................................................................................................................................... 17
S Register 103 - Wireless Link Rate................................................................................................................................................ 17
S Register 104 - Network Address................................................................................................................................................... 18
S Register 105 - Unit Address.......................................................................................................................................................... 18
S Registers 106 and 206 - Primary and Secondary Hopping Patterns.............................................................................................. 18
S Register 107 - Encryption Key...................................................................................................................................................... 20
S Register 108 - Output Power Level............................................................................................................................................... 20
S Register 109 - Hopping Interval.................................................................................................................................................... 21
S Register 110 - Data Format............................................................................................................................................................ 21
S Registers 111 and 112 - Packet Minimum and Maximum Size..................................................................................................... 22
S Register 116 - Packet Character Timeout ...................................................................................................................................... 22
S Registers 113 and 213 - Packet Retransmission/Packet Retry Limit ............................................................................................. 23
S Register 115 - Packet Repeat Interval........................................................................................................................................... 24
S Register 117 - Modbus Mode ........................................................................................................................................................ 24
S Register 120 and 121- RTS/DCD Framing/Timeout ..................................................................................................................... 25
S Register 123 - RSSI Reading......................................................................................................................................................... 25
A. Modem Command Summary...................................................................................................................................................................... 26
B. Serial Interface............................................................................................................................................................................................ 29
C. Sample Schematic Diagram........................................................................................................................................................................ 31
D. Factory Default Settings.............................................................................................................................................................................. 33
EPerformance Tables...................................................................................................................................................................................... 34
F. Hopping Tables............................................................................................................................................................................................ 35
G. Technical Specifications............................................................................................................................................................................. 36
H. Glossary...................................................................................................................................................................................................... 38

MHX-2400 Operating Manual: Chapter 1 Introduction. 1
1. Introduction
1.0 Product Overview
Congratulations on choosing the MHX-2400 wireless transceiver! Your new
MHX-2400 modem is a state-of-the-art, 2.4 GHz frequency-hopping spread-
spectrum communications module. When the MHX-2400 module is
incorporated into the design of new or existing equipment, terminal devices
(DTEs) up to 30 km (or more)1apart will be capable of establishing high-
speed2communications wirelessly.
MHX-2400 modules provide a practical and reliable alternative to using
traditional analog phone-line modems or “permanent wire” serial cable
(RS-232) connections for data communications between asynchronous serial
equipment. Moreover, wireless data communications using the MHX-2400
module means you will benefit from:
ngreater flexibility and freedom to relocate terminal equipment,
neliminated requirement for access to wire-based transfer media
such as telephone lines,
nthe ability to communicate through walls, floors, and many
other obstacles.
While the MHX-2400 module is compact in its design, it delivers power and
convenience and offers quality and dependability. The MHX-2400 module’s
versatility makes it the ideal solution for applications ranging from office-
productivity to industrial data control and acquisition.
While a pair of MHX-2400 modules can link two terminal devices (“point-to-
point” operation), multiple MHX-2400 modules can be used together to
create a network of various topologies, including “point-to-multipoint” and
“repeater” operation. Multiple independent networks can operate
concurrently, so it is possible for unrelated communications operations to
take place in the same or a nearby area without sacrificing privacy,
functionality, or reliability.
1.1 Features
Key features of the MHX-2400 module include:
ntransmission within a public, license-exempt band of the radio
spectrum3– this means that it can be used without access fees
(such as those incurred by cellular airtime);
na serial I/O data port (TTL levels) with handshaking and
hardware flow control, allowing the MHX-2400 module to
interface directly to any microprocessor with an asynchronous
serial interface.
1Ideal conditions with clear line-of-sight communications, using high-gain antennas.
2Up to 115,200 bits per second (bps).
3902-928 MHz, which is license-free within North America; may need to be factory-configured
differently for some countries.

2MHX-2400 Operating Manual: Chapter 1 Introduction
n49 sets of user-selectable pseudo-random hopping patterns,
intelligently designed to offer the possibility of separately
operating multiple networks while providing security, reliability
and high tolerance to interference;
nencryption key with 65536 user-selectable values to maximize
security and privacy of communications;
nbuilt-in CRC-16 error detection and auto re-transmit to provide
100% accuracy and reliability of data;
nease of installation and use – the MHX-2400 module uses a
subset of standard AT style commands, very similar to those
used by traditional telephone line modems.
While the typical application for the MHX-2400 is to provide a short- to mid-
range wireless communications link between DTEs, it can be adapted to
almost any situation where an asynchronous serial interface is used and data
intercommunication is required.
1.2 About this Manual
This manual has been provided as a guide and reference for installing and
using MHX-2400 wireless modem modules. The manual contains
instructions, suggestions, and information which will help you set up and
achieve optimal performance from your equipment using the MHX-2400
module.
It is assumed that users of the MHX-2400 module have either system
integration or system design experience. Chapter 2 details the requirements
and connections of the MHX-2400 module. Chapter 3 describes the AT
command register setup and configuration. The Appendices, including the
Glossary of Terms, are provided as informational references which you may
find useful throughout the use of this manual as well as during the operation
of the wireless modem.
Throughout the manual, you will encounter not only illustrations that further
elaborate on the accompanying text, but also several symbols which you
should be attentive to:
Caution or Warning: Usually advises against some action which could
result in undesired or detrimental consequences.
Point to Remember: Highlights a key feature, point, or step which is worth
noting, Keeping these in mind will make using the MHX-2400 more
useful or easier to use.
Tip: An idea or suggestion is provided to improve efficiency or to make
something more useful.
With that in mind, enjoy extending the boundaries of your communications
with the MHX-2400 module.

MHX-2400 Operating Manual: Chapter 2 Initial Setup and Configuration 3
2. Initial Setup and Configuration
2.0 Unpacking and Inspection
The following items should be found in the shipping carton. Inspect the
contents for any shipping damage. Report damages or shortages to the
distributor from which the unit was purchased. Keep all packing materials in
the event that transportation is required in the future.
Package contents (normal distribution):
1MHX-2400 Wireless Modem module 1
2Operating Manual (this document) 1
2.1 Additional Requirements
Since the MHX-2400 module is a unique product in a class of its own, it will
communicate only with another MHX-2400 module which has been
compatibly configured. Thus, at least two MHX-2400 modules will be
required to establish a wireless communications link.
Additionally, the following requirements should be taken into consideration
when preparing to incorporate the MHX-2400 module in new or existing
designs.
nSmall footprint for the MHX-2400 module (e.g., 2.1” W x 3.5” L
x 0.8” H) on the OEM PCB.
nSerial port and control signals from the host microprocessor.
See sample application schematics in Appendix C.
n+5 Vdc supply from the host OEM electronics.
nAn external antenna (customer supplied).
2.2 Connectors and Indicators
The MHX-2400 module connects to the host equipment by two single row
header strips on the underside of the unit. This enables the MHX-2400
module to be directly soldered or socketed onto the host equipment
manufacturer’s PCB. The pinout for the module is given in Figure 1.

4MHX-2400 Operating Manual: Chapter 2 Initial Setup and Configuration
IMPORTANT:
For best performance, it is
strongly recommended to use
a separate, linearly regulated
supply for Vcc Radio. Do
not directly feed a switching
power supply into Vcc
Radio.
For OEM design simplicity,
connect both the radio and
logic Vcc connections
together.
Caution: Using any other power
supply which does not provide the
proper voltage or current could
damage the MHX-2400 module.
1
20
Top View
Antenna Connector
21
40
Vcc Radio
Vcc Radio
Vcc Logic
N/C
/CONFIG
/RESET
GND
GND
GND
N/C
Tx Mode LED
RSSI LED 3
RSSI LED 2
RSSI LED 1
CTS
RTS
DSR
N/C
DTR
TxD
RxD
DCD
Vcc Logic
Vcc Logic
Vcc Logic
Vcc Logic
GND
GND
GND
GND
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
Rx Mode LED
Figure 1 - Pinout Diagram
The interface connectors and indicator lights are summarized below:
Vcc Radio - These pins supply power for the MHX-2400’s radio circuitry. Best
performance is achieved by providing linearly regulated voltage to these
pins. It is essential to keep this supply rail as clean as possible -
preferrably by not directly feeding a switching power supply into Vcc
Radio. In addition, it is recommended that Vcc Radio be regulated as
close to 5.5V as possible (without exceeding 5.5V). Running from a 5V
regulator will decrease the transmitted power by roughly 1dB. The linear
regulator must be rated for at least 800 mA
Vcc Logic - These pins supply power for the MHX-2400’s digital circuitry. It is
recommended you use a linear regulator to feed Vcc Logic. Current
consumption in the logic circuitry is typically 100 mA. The regulator
should be rated for at least 200 mA. To simplify the OEM design, the
Radio Vcc can be connected to the Logic Vcc.
GND - Ground return pins for both Radio and Logic circuitry
/RESET - This momentary active low input signal (100 ms typical) resets the
MHX-2400.
/CONFIG - Leave this pin unconnected. Do NOT ground.
Receive Signal Strength Indicator (RSSI) - These active high TTL outputs are
designed to drive LED’s. As the signal strength increases, the number of
active RSSI lines increases, starting with RSSI1. When configured as a
Repeater, the module does not indicate RSSI. The LED’s perform a
“scanning” function, blinking on and off in sequence when a Slave or
Repeater modem is searching for synchronization. The current sourcing
capability of these lines is 20 mA.

MHX-2400 Operating Manual: Chapter 2 Initial Setup and Configuration 5
Data Port (DCE) - Pins 21 through 28 inclusive. This port is used to interface
the MHX-2400 module to a DTE device and operates at 2400 to 115,200
bps. The levels are active low 5V logic levels, and include (See
Appendix B for a complete description):
Pin No. Name Description I/O
21 DCD Data Carrier Detect O
22 RxD Receive Data O
23 TxD Transmit Data I
24 DTR Data Terminal Ready I
25 NC No Connect
26 DSR Data Set Ready O
27 RTS Request to Send I
28 CTS Clear to Send O
RX Indicator - This active high output indicates the modem is receiving data
packets with correct CRC, and is designed to drive a LED. When the unit
is configured as a Slave, this LED will typically be on solid under good
operating conditions.
TX Indicator - This active high output is designed to drive a LED, and indicates
the modem is transmitting.
Antenna Connector - The MHX-2400 uses an end launch SMA RF
connector. Microhard Systems can provide the cabling from the
module to the appropriate antenna connector. A suitable antenna must
be used to ensure adequate performance of the MHX-2400 module.
N/C - These pins are reserved for future use. Do not connect to these pins.

6MHX-2400 Operating Manual: Chapter 2 Initial Setup and Configuration
MS
Network 1
MSR MSR
Network 2
M
S
S
S
Network 3
MR
S
S
S
Network 4
MR
SR
S
Network 5
Figure 2 - Sample Network
Topologies. Virtually any
Combination of Slaves and
Repeaters May be Used.
2.3 Configuration
Prior to establishing a wireless link, each MHX-2400 module participating in
the link must be correctly configured for compatibility and for the desired
mode of operation.
Network topologies consisting of a single Master and virtually any
combination of Slaves and Repeaters may be deployed. The functionality of
any particular MHX-2400 can be configured as follows:
nMaster Point-to-Point: The module is configured to
communicate with a single Slave, either directly, or through one
or more Repeaters.
nMaster Point-to-Multipoint: The module is configured to
communicate with one or more Slaves and/or Repeaters.
nSlave: The module is configured to communicate with one
particular Repeater or Master.
nRepeater: The module is configured to pass information from
either a Master or another Repeater onto subsequent Repeaters
and/or Slaves and vice versa. The Repeater also acts as a Slave
in the sense that, like a Slave, it passes information to/from its
serial port.
All units within a network must be assigned a common Network Address;
thus enabling multiple networks to co-exist in the same vicinity without
unwanted crosstalk between modules. Examples of different network
topologies are shown in Figure 2. Network 1 shows Point-to-Point
communication between a Master and Slave. Network 2 makes use of a
Repeater to communicate with the Slave. Network 3 illustrates a simple
Point-to-Multipoint network with no Repeaters. Networks 4 and 5 gives
examples of Point-to-Multipoint networks consisting of both Repeaters and
Slaves. There is effectively no restriction to the number of Repeaters and
Slaves that can be added to a network. As seen in Network 4, a Master can
communicate directly with both Slaves and Repeaters. The MHX-2400 has
been designed to allow for additional Repeaters and Slaves to be added to an
existing network without having to reconfigure any units already in the
network. This saves a tremendous amount of time when deploying additional
units in the field.
2.3.1 Quick Start Approach
The MHX-2400 is equipped with four standard factory default settings.
Instead of manually configuring each individual operating parameter, a global
command may be used to quickly configure the modem for a particular type
of operation. For example, to quickly implement Network 1, Factory default
1 would be applied to the Master, and Factory default 2 would be applied to
the Slave. To quickly set up Network 2, apply Factory 1 to the Master,
Factory 3 to the Repeater, and Factory 4 to the Slave. These defaults will get
you started and only ensure that a link can be established, but do not
necessarily provide the best performance. Optimization of the
communications link is discussed in later sections.

MHX-2400 Operating Manual: Chapter 2 Initial Setup and Configuration 7
Warning: Using an antenna that
is inappropriate for use with the
MHX-2400 module could result in
undesired performance, and may
damage the unit. It is the user’s
responsibility to ensure the
antenna has adequate lightning
protection.
How to Set Up A Simple Network
The MHX-2400 will always be in one of two states:
nData Mode – When in this state, the modem is listening and talking
to other modems in the network (the modem is online).
nCommand Mode – When in this state, the modem is awaiting “AT
Commands” from the serial port. These commands are used to
configure all operating parameters of the modem. When in this
state, the modem is “offline”.
To implement the very basic network illustrated in Figure 2, Network 1,
nPlug the modem into the development board and connect a straight-
through serial cable between the development board and the
terminal (e.g., your PC)
nConnect an antenna cable and antenna to the module.
nConfigure the unit to Factory Setting 1 by typing AT&F1 <return>.
This puts the unit into Master Point-to-Multipoint mode.
nStore these settings to memory by typing AT&W <return>.
nPut the modem into Data Mode by typing ATA <return>. There are
other ways to enter Data Mode, which are discussed in Chapter 3.
nPerform the above steps for the second unit, using the command
AT&F2 instead of AT&F1. This will configure the second unit as a
Slave.
The units should now be communicating. Remember, the parameters defined
by AT&F1 and AT&F2 will likely not be the most ideal for your application,
but will quickly allow you to test the units. A complete summary of the
settings defined by AT&F1,2,3 and 4 can be found in Appendix D. Factory
Default Settings.
Settings are not immediately stored in non-volatile memory, therefore, the
command &W is issued to store the current configuration into non-volatile
memory. Settings are retained even after powering down. All user selectable
parameters for the MHX-2400 are described in detail in Chapter 3:
Configuration Options.
2.4 Checking the Link
To check if the units are communicating, observe the LED indicators on the
development board. If the link is good, up to three RSSI outputs on the Slave
modem should be active; and if the link is absent (due to a fault at one end or
another, such as misconfiguration), the outputs will be in either “scanning
mode” or inactive.
Characters typed at the Master terminal should appear at the Slave’s terminal,
and vice versa. Also, verify that the RX LED blinks as packets of data are
received at the Master modem. As data is sent from Slave to Master, the RX
indicator should blink on as correct packets of data are received. It is
recommended that if MHX-2400 modules will be deployed in a field where
large distances separate the units, the modems should be configured and
tested in close proximity (e.g., in the same room) first to ensure a good link
can be established and settings are correct. This will facilitate
troubleshooting, should problems arise.

8MHX-2400 Operating Manual: Chapter 3 Configuration Options
3. Configuration Options
The escape sequence will not
be accepted unless both the
MHX-2400 and the terminal
are set to the same baud rate
Refer to Appendix A (page
19) for a summary of the
modem commands
Configuration options are
not stored in non-volatile
memory until the WRITE
command (&W) is executed
3.0 Command Line Interface
The MHX-2400 modem can be easily configured to meet a wide range of
needs and applications. You can have your modem perform a variety of
functions by sending it instructions (in the form of commands). Sending a
command overrides the modem’s operating characteristics.
Your modem must be in Command Mode for it to execute a command. If
you send characters when the modem is in Data Mode, the modem transmits
the characters over the air.
Depending on its settings, the modem will either power up in Command
Mode or Data Mode. Normally, when first received from the factory, the
unit will power up in Command Mode.
You can place the modem into Data Mode either by
1. Issuing the answer command
2. Issuing the online command
You can place the modem into Command Mode either by
1. Sending the escape sequence
2. Toggling the DTR line (depending on the &D parameter see pg 11).
To enter a command line and have your modem execute it, use the following
procedure:
1. With your modem in the Command Mode, type AT. These characters,
known as the attention characters, must be typed at the beginning of
each command line.
2. Type the command(s). Include any parameters required by the
command. To make the command line more readable, you can insert as
many spaces as desired. The command line holds up to 16 characters,
not including the AT prefix.
3. Press the ENTER key. Your modem executes the command line and
sends you a word response (usually OK).
For example, to set the Operating Mode S101 register to Master Point-to-
Multipoint mode, enter the following command line; AT S101 = 1 <return>.
To display what a register is currently set to, enter the following command
line; AT Sxxx? <return>. The modem will output the value of the register.

MHX-2400 Operating Manual: Chapter 3 Configuration Options 9
Note: If you want to send more than one command line, wait for a response
before entering the AT prefix at the start of the next command line.
To re-execute the previous command, enter A/. The modem will execute
the previous command line.
When in Command Mode, the modem “autobauds”, meaning that it will
automatically adjust to the baud rate of the terminal. You may change the
terminal baud rate while in Command Mode without losing communication
with the modem.
For the AT command protocol, an escape sequence consists of three
consecutive escape codes preceded and followed by at least 1 second of
inactivity. Typically, the ‘+’ character is used as the escape code.
+++ preceded and followed by 1 second of inactivity
Note that the terminal must be configured to the same baud rate as the
modem in order for the mode to recognize the escape sequence. The
modem is unable to “autobaud” while in Data Mode.
3.1 AT Commands
Several AT Commands are supported by the MHX-2400 module. The
following is a short description of all available commands. ‘*’ denotes
standard factory settings. All of the following commands must be preceded
by “AT”
AAnswer
The A command causes the modem to attempt to connect with another
remote modem (Type ATA <return>).
ECommand Echo
Your modem is preset to return (or echo) commands to the host
microprocessor when in Command Mode.
E0 No Command Echo
*E1 Command Echo
IIdentification
The I command returns various modem information settings.
I1 Product Code (MHX-2400)
I2 Issue ROM Check (OK or ERROR)
I3 Product Identification (Firmware Version)
I4 Firmware Date
I5 Firmware Copyright
I6 Firmware Time
I7 Serial Number

10 MHX-2400 Operating Manual: Chapter 3 Configuration Options
OOn-line Mode
The O command attempts to put the modem online and communicate with a
remote modem.
QQuiet Mode
Your modem is preset to send responses when it executes commands, and
there after to keep the host informed of its status.
*Q0 Enable modem responses
Q1 Disable modem responses
VResult Codes display
Your modem can either display result codes as words or numbers.
V0 Display Result Codes as numbers
*V1 Display Result Codes as words
WConnection Result
The W command returns your modem to the Data Mode from the Command
Mode
*W0 Reports computer (DTE) baud rate as CONNECT xxxx
W1 Reports computer (DTE) rate and wireless rate between
modems as CARRIER xxxx.
W2 Reports modem (DCE) baud rate as CONNECT xxxx
ZReset and load stored configuration
The Z command resets the modem and loads the stored configuration.
&C DCD (Data Carrier Detect)
The &C command controls the modem’s DCD output signal to the host
microprocessor. This command determines when the DCD is active.
&C0 DCD is always ON
*&C1 DCD on when modems are synchronized. DCD is always
on when unit is configured as Master.
&C2 DCD used for output data framing and Modbus mode.
See page 25 for details.
&D DTR (Data Terminal Ready)
The &D command controls what action the modem performs when the DTR
input line is toggled. The DTR input is controlled by the host
microprocessor.
*&D0 DTR line is ignored
&D1 Not Supported
&D2 DTR disconnects and switches to Command Mode
&D3 DTR disconnects and resets modem. Modem will remain
in this state until DTR again goes active.

MHX-2400 Operating Manual: Chapter 3 Configuration Options 11
&F1 &F2
Master Slave
&F1 &F4
&F3
Master Repeater Slave
&F Load Factory Default Configuration
The &F command resets the modem and loads the default factory
configuration.
&F1 Master Point-to-Multipoint. Designed to communicate
with modems configured as &F2 or &F3.
&F2 Slave. Designed to communicate with another modem
configured as &F1.
&F3 Repeater. Designed to communicate with modems
configured as &F1 and &F4.
&F4 Slave working with factory default Repeater and factory
default Master. Communicates directly with Repeater
configured as &F3.
&K Handshaking
The &K command controls the handshaking between the modem and host
microprocessor.
&K0 Disable handshaking
&K2 RTS/CTS input data framing. See page 25 for details.
*&K3 Enable hardware handshaking (RTS/CTS)
&S DSR (Data Set Ready)
The &S command controls the DSR line for the modem, and determines
when it is active
&S0 DSR is always ON
*&S1 DSR is ON in Data Mode, OFF in Command Mode
&V View Configuration
The &V command displays the current (DTE) baud rate, and all setable
modem parameters including S register values.
&E Framing Error Check
This command enables or disables Framing Error Check. When enabled,
the modem looks for the stop bit. If the stop bit is absent, the byte is thrown
out. When enabled, the modem also does a parity check. Note that the data
format (number of data bits, parity type, and number of stop bits) is defined
by S register 110.
*&E0 Disable Framing Error Check
&E1 Enable Framing Error Check
&W Write Configuration to Memory
The &W command stores the active configuration into the modem’s non-
volatile memory.
Sxxx? Read S register value
This command causes the modem to display the current setting of S register
xxx.
Sxxx=yyy Set S register value (see section 3.3 S-Registers)
This command sets the specified S register to a value specified by yyy.

12 MHX-2400 Operating Manual: Chapter 3 Configuration Options
3.2 Command Result Codes
The MHX-2400 module can either display the results of a command as
either text strings or numerical data. The following chart shows resulting
text string and corresponding numeric result.
0OK
3NO CARRIER
4ERROR
7CONNECT 2400
8CONNECT 3600
9CONNECT 4800
10 CONNECT 7200
12 CONNECT 9600
13 CONNECT 14400
14 CONNECT 19200
15 CONNECT 28800
17 CONNECT 38400
18 CONNECT 57600
33 CONNECT 115200
62 CARRIER 45000
64 CARRIER 20000

MHX-2400 Operating Manual: Chapter 3 Configuration Options 13
S Registers 2 through 5
cannot be stored to non-
volatile memory.
3.3 S Registers
S Register 0 - Auto Answer
If this register is set to zero, the modem will power up in command mode. If
this register is non-zero, the modem will power up in data mode.
S Register 2 - Escape Code
This register contains the ASCII value of the escape character.
The default value (decimal 43) is equivalent to the ASCII character ‘+’.
Values greater than 127 disable the escape feature and prevent you from
returning to the Command Mode. This register cannot be stored to non-
volatile memory. If the modem is reset, or powered down, the default value
is restored.
Default is ‘+’ (decimal 43).
S Register 3 - CR Control Code
This register contains the ASCII value of the carriage return character.
This is the character that is used to end the command line and is also the
character that appears after the modem sends a response. This register
cannot be stored to non-volatile memory. If the modem is reset, or powered
down, the default value is restored.
Default is ‘CR’ (decimal 13).
S Register 4 - Linefeed Control Code
Register S4 sets the ASCII value of the linefeed character.
The modem sends the linefeed character after sending a carriage return
character when sending text responses. This register cannot be stored to
non-volatile memory. If the modem is reset, or powered down, the default
value is restored.
Default is ‘LF’ (decimal 10).
S Register 5 - Backspace Control Code
Register S5 sets the ASCII value of the backspace character.
This character is both the character created by entering BACKSPACE and
the character echoed to move the cursor to the left. This register cannot be
stored to non-volatile memory. If the modem is reset, or powered down, the
default value is restored.
Default is ‘BS’ (decimal 8).

14 MHX-2400 Operating Manual: Chapter 3 Configuration Options
Only one Master can exist
for each network.
S Register 101 - Operating Mode
The Operating Mode (register S101) partly defines the “personality” of the
MHX-2400 module. Allowable settings for this register are 1 through 4 as
follows:.
• S101=1 Master Point to Multipoint
• S101=2 Master Point to Point
• S101=3 Slave
• S101=4 Repeater
The default for this register depends on which factory default is selected as
shown below:
• Default for Factory Setting &F1 is 1 (Master Point-to-Multipoint)
• Default for Factory Setting &F2 is 3 (Slave)
• Default for Factory Setting &F3 is 4 (Repeater)
• Default for Factory Setting &F4 is 3 (Slave)
1)Master - Point to Multipoint. In any given network, there
is always only one Master. All other units should be configured as either
Slaves or Repeaters. When defined as a Point-to-Multipoint Master, the
modem broadcasts data to all Slaves and Repeaters in the network, and is
also the ultimate destination for data transmitted by all Slaves and
Repeaters. In addition, the Master defines the following network parameters
to be utilized by all other modems in the network (See the appropriate
sections for a complete description of these parameters):
nMaximum Packet Size (S112)
nMinimum Packet Size (S111)
nWireless Link Rate (S103)
nHop Interval (S109)
2)Master - Point to Point. This mode of operation is identical
to Master Point-to-Multipoint, with the exception that the Master only
broadcasts to one particular Slave or Repeater. The modem with which
communication occurs is defined by the Unit Address (S105). For example,
if a Slave has been assigned Unit Address 100, and the Master wishes to
communicate with that Slave, the Master must also be assigned a Unit
Address of 100. If there are Repeaters in the network, they will pass the
packet through to the Slave, and vice versa. Because Repeaters also have
Slave functionality (i.e., a Repeater can be connected to a terminal), the
Master can choose to communicate solely with a Repeater. This would be
accomplished by assigning the same Unit Address to both the Master and
the Repeater.

MHX-2400 Operating Manual: Chapter 3 Configuration Options 15
PHP=1 PHP=2
PHP=1
SHP=2
Master
Repeater
Slave
Network 50
Hop Pattern 1
Hop Pattern 2
Figure 3 - Repeater
Operation
Master Repeater
Slave
Repeater
Slave
PHP=1 PHP=1
SHP=2
PHP=2
PHP=2
SHP=3 PHP=3
Hop-
Pattern 1
Hop Pattern 2
Hop Pattern 3
Figure 4 - A Network
Utilizing Three Hopping
Patterns
If there is no DTE connected
to the Repeater, turn off
handshaking (&K0) and set
the baud rate to 115K.
3)Slave. Up to 65534 Slaves may exist in a network, all of which
communicate with the common Master (either directly or via Repeater(s)).
Slaves cannot directly communicate with other Slaves, nor can they
acknowledge packets of data sent by the Master. Clearly this would cause
conflicts when there are multiple Slaves. The Master does, however, send
acknowledgements to all messages it receives from Slaves. The Master
initiates communications by sending a broadcast message to all Slaves. All
Slaves are free to respond in a “Slotted ALOHA” fashion, meaning that each
Slave can choose one of several windows in which to transmit. If there
happens to be two Slaves attempting to talk at the same time, the Master
may not receive the data, and the Slaves therefore would not get an
acknowledgement. At this point, the Slaves would attempt to get the
information through at random time intervals, thus attempting to avoid any
more conflicts. Special parameters which control the Slave’s response
characteristics can be modified with S Registers S115 and S213.
4) Repeater. A more precise title would be Repeater/Slave, because a
Repeater also has much of the same functionality as a Slave. A terminal can
be connected at the Repeater location and communicate with the Master
terminal. There is no restriction to the number of Repeaters in a network,
allowing for communication over virtually limitless distances. The presence
of one Repeater in a network automatically degrades system throughput by
half. Additional Repeaters, regardless of the quantity, do not diminish
system throughput any further. To understand Repeater operation, consider
the module as belonging to two hopping patterns at the same time: The
Primary Hopping Pattern and the Secondary Hopping Pattern. In Figure 3,
the Master belongs to Hopping Pattern 1, and communicates with the
Repeater on this hopping pattern. The Slave belongs to Hopping Pattern 2,
and communicates with the Repeater on this hopping pattern. The whole
system belongs to Network 50 (i.e., all units must be assigned the same
Network Address (S104), which in this case was selected to be 50. Note
that Slaves and Master only communicate on their respective Primary
Hopping Pattern. Repeaters communicate on the Primary Hopping Pattern
when communicating with the Master (or with another Repeater between
itself and the Master). Repeaters communicate on their Secondary Hopping
Pattern when communicating with Slaves (or with another Repeater between
itself and the Slaves). Figure 4 shows another example.
If the Repeater is not also being used as a Slave (there is no DTE connected
to the serial port), it is recommended that the Repeater’s baud rate be set to
115K, and that handshaking be disabled (&K0). This will help ensure a
smooth flow of data through the network.

16 MHX-2400 Operating Manual: Chapter 3 Configuration Options
The Master determines the
Wireless Link Rate. This
setting on all other modems
is ignored..
S Register 102 - Serial Baud Rate
The Serial Baud Rate is the current speed that the modem is using to
communicate with the DTE. When the AT command prefix is issued, the
modem performs an ‘autobaud’ operation and determines what the current
DTE baud rate is set to. The S register value returns the current setting of
the DTE baud rate.
The possible values are:
* 1 115200
2 57600
3 38400
4 28800
5 19200
6 14400
7 9600
8 7200
9 4800
10 3600
11 2400
It is generally advisable to choose the highest rate that your terminal
equipment will handle to maximize performance, unless a limitation on the
available bandwidth is desired. If the DTE is a personal computer, the port
can usually be used reliably at 115200. It is not possible to write values to
this register, since the instant another AT command is issued, the register
will revert to the current baud rate. Therefore, it is advisable to operate in
Command Mode at the desired baud rate for Data Mode.
S Register 103 - Wireless Link Rate
The Wireless Link Rate is the speed and optimization method for which
modems will communicate over the RF link. It is only necessary to set this
parameter on the Master unit. Units configured as Repeaters and Slaves will
ignore this setting, and adjust automatically to the rate of the Master.
The allowable settings are:
2Fast without Forward Error Correction
*4Fast with Forward Error Correction
Depending on the application requirements, each mode will provide
different throughput and performance. Appendix E. Performance Tables
give some indication of the performance to be expected in each mode.
In general, Forward Error Correction (FEC) reduces throughput, but in some
environments will actually increase throughput. FEC can reduce the number
of bad data packets, and hence reduce the need to retransmit.