GDI SM2400 User manual

MODEL SM2400
2400 BAUD
DIAL-UP MODEM
SMART MODEM
USER GUIDE
280 Interstate 80 West Exit 1 / PO Box 1330, Verdi NV 89439
Phone: [phone] Fax: [phone] E-mail: [email protected]

PROPRIETARY DATA
This document contains confidential, proprietary data with all rights
and titles reserved by GDI Communications LLC. By accepting
this document, the recipient assumes custody hereof and agrees not
to disclose this data or any portion of this data to any unauthorized
person without the prior written consent of GDI Communications
LLC. Recipient further agrees not to incorporate these drawings,
specifications or technical information, in whole or in part, in any
other product or endeavor.
THIS LEGEND SHALL BE INCLUDED ON
ANY REPRODUCTION OF THIS DOCUMENT

GDI Communications LLC
MODEL SM2400
Smart Modem
Revision B-2.0
USERS MANUAL
GENERAL
The GDI Model SM2400 is a Hayes compatible Dial-up modem, designed for plug-in
compatibility with 170 series Traffic Controllers. It is intended to allow, with proper
software support, communication between a 170 and a host computer over standard dial-
up or leased telephone lines. The GDI Model SM2400 includes a modulator, demodulator,
filters, phone line interface, and 170 controller interface. It offers 300/1200/2400 baud
transmission & reception, auto-dial/-answer/-speed detect, and Hayes command set
compatibility, all on a single board with the standard Model 400 form factor.
In addition to all of the features normally found in a Hayes-compatible modem, the GDI
Model SM2400 is fully temperature tested.
FEATURES
- Form factor consistent with the standard Model 400.
- Front edge mounted status indicators.
- Industry standard 'AT' command set.
- Auto-Dial Auto-Answer Auto-speed detect.
- Highly flexible configuration options.
- Fully temperature tested.
- Configuration options stored in NVRAM - no jumpers.
- Call progress monitor speaker.
- May be cable connected to auxiliary ACIA

TABLE OF CONTENTS PAGE
GENERAL CHARACTERISTICS …………………………………………………3
INSTALLATION ……………………………………………………………………6
SHIPPING CONFIGURATION…………………………………………………… 7
ADJUSTMENTS…………………………………………………………………… 7
THEORY OF OPERATION ……………………………………………………… 8
System Description ………………………………………………………… 8
Description of Circuit Operation…………………………………………… 9
MAINTENANCE………………………………………………………………… 10
Preventive Maintenance…………………………………………………... 10
Alignments………………………………………………………………… 10
Trouble Analysis…………………………………………………………... 10
Special Considerations…………………………………………………….. 10
Waveforms and Voltage Measurements……………………………………10
TEST PROCEDURE……………………………………………………………….11
COMMAND SET…………………………………………………………………. 12
CONFIGURATION (S) REGISTERS……………………………………………. 24
PROGRAMMABLE OPTIONS NOT SAVED IN NVRAM……………………. 30
PROGRAMMABLE OPTIONS SAVED IN NVRAM………………………….. 30
COMMAND SUMMARY………………………………………………………... 31

General Characteristics
INDICATORS TXD Transmitted Data
RXD Received Data
OH Off Hook, on when modem is off hook
DTR Terminal Ready, on when host is ready
HS High Speed, on when in 2400 baud mode
DCD Carrier Detected
AA Originate/Answer mode, on when in answer mode
OPERATING TEMPERATURE RANGE
-30°C to +70°C
HUMIDITY
95% Relative Humidity, non-condensing
LINE REQUIREMENTS
(a) Public switched telephone network
(b) Private unconditioned leased lines
MODES OF OPERATION
Asynchronous
Full or half duplex
Automatic and manual call originate Automatic and manual call answer
COMPATIBILITY
CCITT V.22 bis, V.22 A&B, V.21, Bell 212A and Bell 103 Automatically adapts to
calling or called modem
ASYNCHRONOUS DATA RATES
2400 and 1200 bps, character asynchronous 0 - 300 bps asynchronous
ASYNCHRONOUS CHARACTER FORMAT
Character length of 8, 9, 10 or 11 bits Parity - odd, even, mark, space or none
ASYNCHRONOUS OVERSPEED/UNDERSPEED RANGE
Nominal rate -2.5% to +1.25% in character asynchronous mode Data formatter follows
CCITT V.22 bis and Bell 212A
TELEPHONE LINE INTERFACE
Meets FCC part 68 requirements
Maximum transmit level -9dBm (600 fl) Two wire full duplex. Uses TIP and RING
MODULATION
V.22 bis - 16 Level Quadrature Amplitude Modulation (QAM)
V.22 and 212A - 4 Level Differential Phase Shift Keying (DPSK)
V.21 and 103 - Phase-Coherent Frequecy Shift Keying (FSK)

TRANSMIT CARRIER FREQUENCIES
V.22 bis:
V.22:
212A: ORIGINATE 1200 Hz +/- 0.01%
ANSWER 2400 Hz +/- 0.01%
V.21 @ 300 bps:
ORIGINATE ‘ space’ 1180 Hz +/- 0.01%
ORIGINATE ‘ mark’ 980 Hz +/- 0.01%
ANSWER ‘ space’ 1850 Hz +/- 0.01%
ANSWER ‘ mark’ 1650 Hz +/- 0.01%
Bell 103:
ORIGINATE ‘ space’ 1070 Hz +/- 0.01%
ORIGINATE ‘ mark’ 1270 Hz +/- 0.01%
ANSWER ‘ space’ 2020 Hz +/- 0.01%
ANSWER ‘ mark’ 2225 Hz +/- 0.01%
LINE EQUALIZATION
(a) Fixed compromise equalization in transmitter
(b) Adaptive equalizer for 1200 and 2400 bps in receiver
INTERFACE SIGNALS
RS232C levels with CCITT V.24 protocols
AUTODIALER TYPE
DTMF or pulse type dialing, specified in commands
DTMF TONE PAIR BALANCE
Better than 3dB
DTMF TONE DURATION AND SPACING
Variable from 50 to 255 milliseconds (Register S11)
Default duration 100 milliseconds
PULSE DIALING RATE
10 pulses per second
PULSE DIALING DUTY CYCLE
39/61% (US) or 33/67% (UK Hong Kong) make/break ratio
PULSE DIALING INTERDIGIT INTERVAL
650 milliseconds
BILLING DELAY INTERVAL
2 seconds silent time, before answer tone

GUARD TONES
Guard tones of 1800 Hz or 550 Hz may is transmitted by the answering modem, for echo
suppression. Default - no guard tone. Guard tone will not be transmitted in Bell 212A or
103 modes.
COMMAND BUFFER SIZE
40 Characters maximum, which includes the required carriage return. The modem does
not count the required AT prefix.
FAILED CALL TIMER
2-255 seconds (Defaults to 30 seconds)
RESULT CODES (TO TERMINAL OR 170)
Ability to limit, abbreviate, or suppress codes
RECEIVE CARRIER DETECT
Off-to-On Threshold: -43 dBm On-to-Off Threshold: -48 dBm
Hysteresis: Greater than 2 dB
TIMING
Request to send-Clear to send Delay
As per CCITT and BELL protocols during modem handshaking.
Delay specified by register S26. (default 10 mS)
TIMING
DCD ON delay
As per CCITT and BELL protocols (600 mS)
TIMING
DCD OFF delay
52.5 +/- 12.5 mS at 2400,1200 bps
17 +/- 7 mS at 300 bps
PERFORMANCE
Bit Error Rate of 1 bit per 100,000 for a S/Noise Ratio of 10dB
TxD Level -10 dBm
RxD Level -45 dBm
POWER
+12 Volts +/- 5% at 200 mA
-12 Volts +/- 5% at 200 mA
170 CONTROLLER INTERFACE
ETA RS-232-C via standard 400 modem edge connector pinout or a 9 pin Male D-Sub
connector J14, user selectable.

J14 PINOUT (9 PIN MALE RS232)
Pin Function Direction
1 DCD (Data Carrier Detected) Output
2 RXD (Received Data) Output
3 TXD (Transmitted Data) Input
4 DTR (Data Terminal Ready) Input
5 GND (Signal Ground) Common
6 DSR (Data Set Ready) Output
7 RTS (Request To Send) Input
8 CTS (Clear To Send) Output
170 EDGE CONNECTOR PINOUT
Pin Function
A & B Signal Common (DC Ground)
C & D +12 Volts
E & F -12 Volts
K DCD (Data Carrier Detected)
L RTS (Request To Send)
M TXD (Transmitted Data)
N CTS (Clear To Send)
P RXD (Received Data)
TELCO CONNECTOR PINOUT (LINE)
Pin Function Direction
4 TIP TERMINAL To/From RJ11C jack
3 RING TERMINAL To/From RJ11C jack
INSTALLATION
Before installing the Model SM2400, it is necessary to determine if the controller
application software expects to talk to the Smart Modem via ACIA1 (modem slot and C2)
or ACIA2 (C20 only). If the software communicates with the smart modem via ACIA1,
installation consists of simply plugging the modem into the modem slot and connecting
the phone line to the modular jack (LINE). If the softwar talks to the Smart Modem
through ACIA2 (C20), it is necessary to remove the jumper arrangement plugged into J3
(Edge Connector Enable) and supply a cable between C20 and the 9 pin connector of the
modem (J14). One can then plug in the modem and connect the phone line.
If you have completed the steps in the above paragraph and are still experiencing
problems you are encouraged to contact your software supplier and/or GDI. The Model
SM2400 is shipped from the factory in the most commonly used operating configuration
but some software suppliers require different operating options that can be accommodated
by reconfiguring non-volatile RAM.

ADJUSTMENTS
NVRAM
The Model SM2400 is equipped with Non Volatile Random Access Memory. This
memory stores modem operating parameters even when power is off. Two complete User
Profiles and four Dialing Strings may be stored. This eliminates the need for jumper
arrangements while allowing more flexibility. A detailed description of which parameters
are stored in this memory and how to alter its contents is given in the Command Set
section.
Switches
The GDI Model SM2400 has an eight position DIP switch (SW1) that is used to 'strap'
operating parameters. Only positions 1 through 6 are used. The following is a description
of their function.
Switches 1 through 4 - TXn
These switch positions are used to adjust transmit levels. They are preset at the factory
and should NOT be change
user as doing so may cause a violation of FCC regulations and/or compromise
performance. If these switches are inadvertently altered, restore them to: switch 1 ON,
Switches 2,3,4 OFF
Switch 5 - BELL/CCITT
This switch position has been superseded by an enhanced "B" command. It should be left
in the "OFF" condition.
Switch 6 - Dumb/Smart
If switch 6 is OFF the modem will ignore commands and refrain from sending result
codes to the terminal (Dumb mode). To use the dumb mode, first store operating
parameters in NVRAM, then turn switch 6 OFF. At the next power up the modem will
assume the dumb mode. Turn switch 6 ON and power up to reestablish Smart mode.
(factory default ON)
SHIPPING CONFIGURATION
The modem is shipped from GDI in a slightly different configuration than described in the
command &F. This is for compatibility with most 'traffic' software. The differences are:
1200 baud instead of 2400 baud communication rate, and Auto-Answer enabled.
To restore the modem to shipping configuration:
1. Connect to 1200 baud terminal, power off, back on.
2. AT&F <return> fetch factory profile
3. AT&C0&D1 <return> DCD and DTR options
3. ATS0=1 <return> Auto-Answer enabled (first ring)
4. AT&W0 <return> Write current profile to NVRAM

THEORY OF OPERATION
System Description
The Model SM2400 modem is designed to provide the Traffic Industry with the
advantages of a Hayes compatible Dial-up modem, while minimizing limitations imposed
by connecting it to a 170's 6850 Asynchronous Communications Interface Adapter
(ACIA). The 6850 RS-232-C control lines are not sufficient in number to provide
complete control over an off-the-shelf Hayes modem. The 170 communication signal
lines, available at the C2S and/or C2OS connectors, consist of the following:
RS-232 170
NAME DESIGNATION DESIGNATION ORIGIN FUNCTION
TXD BA PIN K (DI) 170 Digital data input
RXD BB PIN L (DO) Modem Digital data output
from modem
CTS CB PIN M (CTS) Modem Flags the 170 that the
modem is ready to
transmit data
RTS CA PIN J (RTS) 170 Signals the modem that
the 170 wants to
transmit
DCD CF PIN H (CD) Modem Flags the 170 that a
carrier signal is being
received
GND AB PIN N (GND) Both Circuit common
An off-the-shelf Hayes modem minimally requires the following additional signal lines to
implement full operation, for which support from a 170 ACIA is not available:
NAME DESIGNATION ORIGIN FUNCTION
DSR CC Modem Indicates that the modem is ready to
transfer data.
DTR CD Host Indicates to modem that host is ready
to communicate.
The Model SM2400 solves this problem by essentially ignoring DTR (See Configuration
Command &D). The factory default for DSR is always on (See &S). Since DSR is not
monitored by the 170, this only becomes an issue when the Model SM2400 is connected
to Data Terminal Equipment.
From a system perspective, the modem has basically three interfaces With the outside
world.
1. Power Supply Edge Connector P1
2. RS-232 Edge Connector P1 or DB-9 J14
3. Phone Line RJ11-C Connector "LINE"

DETAILED CIRCUIT DESCRIPTION
The GDI Model SM2400 consists of 6 basic functional blocks (figure 2). They are the
power supply section, the DAA (Data Access Arrangement), analog front end, application
specific processor, NVRAM, and the RS-232 interface section. The following discussion
describes their operation.
Power Supply
The power supply section is where all voltages necessary for operation of the modem are
derived. The voltages required on the Model SM2400 board are +12, -12, +5, & -5 volts.
The +/- 12 volts is obtained via the edge connector of the Model SM2400. VR1 regulates
the +12 volts to produce a regulated +5 volts. VR2 regulates the -12 volts to produce a
regulated -5 volts.
DAA
This is the telephone line interface. Its functions are:
1. Comply to impedance and isolation requirements.(FCC part 68)
2. Furnish a method of switching between the modem and an optional telephone handset.
3. Provide for on/off hook control as well as pulse dialing.
4. Ring detection.
The FCC has stringent rules regarding the characteristics of devices connected to public
telephone networks. These are detailed in Part 68 of the Code of Federal Regulations.
Transformer Tl presents the proper impedances to the telephone line while isolating the
TIP and RING signals from the analog front end. Opto-coupler U10 is the isolating
element of the ring detector subsection of the DAA. Relay K2 allows isolated switching of
the phone line between the modem and an optional handset under modem control. Relay
Ki allows isolated on/off hook control and a mechanism for pulse dialing.
Analog Front End
The purpose of the analog front end is to:
1. Perform complex receive and transmit filter functions.
2. Synthesize transmitted signals (programmable levels).
3. Provide system master timing source.
The core of the analog front end is the 89027 chip (U1). The filter functions are performed
internally using CMOS switched capacitor technology. Transmitted signal synthesis is
achieved using digital to analog conversion techniques. An internal oscillator in
conjunction with crystal Y1 furnishes the master timing source. Signals connected
between Ui and U2 (application specific processor) form a digital serial link that allow the
two system elements to 'talk' back and forth.
Application Specific Processor
The application specific processor (89026 U2) performs all of the 'intelligent' functions of
the modem. Its functions are:
1. Analyze and execute commands.
2. "Control/monitor DAA.
3. Support NVRAM.
4. DTE handshaking functions.
5. Relay information to/from analog front end.

The 89026 is a high speed 16 bit microcontroller in a 68 pin PLCC package. Its program,
residing in internal masked ROM, controls all modem functions. It is a self contained,
single chip, device that needs only a clock (provided by Ul) and power to operate.
NVRAM
NVRAM stands for Non Volatile Random Access Memory. Its purpose is to retain
important configuration options even while power is off. This design uses a serial device
(93C46 U3). The system controller (U2) modifies the contents of this device in
accordance with software configuration commands (&Wn).
RS-232 Interface
This section furnishes level conversion (TTL to RS-232), connection options, and status
indicators. U7 is an RS-232 receiver (1489) while U8 is an RS-232 line driver (1488). J3
is a shunt arrangement that, when removed, 'disconnects' the modem from the edge
connector (P1). This option is useful when cable connection (via J14) is desired. Level
translator/buffer U8 (2588) allows the status indicator LED's to be driven from the -12V
supply. This reduces current consumption on the positive supply, making the two a little
more symmetrical.
MAINTENACE
Preventive Maintenance
This device requires no preventive maintenance.
Alignments
This modem is self aligning using a technique called adaptive equalization.
Trouble Analysis
The G.D.I. Model SM2400 is fully tested over temperature prior to shipment, however,
rare circuit failures do occur for a variety of reasons. A Troubleshooting Flowchart and a
written Test Procedure are included to aid in fault isolation. Also, it should be noted that,
many "problems" are caused by improper connections and/or noisy phone lines.
Trouble Analysis Special Considerations
All modems that are intended to connect to dial-up lines are required to conform to FCC
part 68 regulations. This means special testing by the manufacturer must be performed to
ensure compliance. For this reason GDI recommends that no attempt at repairing the
DAA section of the modem should be made by the user.
Waveforms and Voltage Measurements
The modem is purely digital in nature. All logic signals conform to TTL standards. All
serial I/O signals conform to RS232 standards. Voltage measurements of the power
supplies should be within 5% of nominal.

TEST PROCEDURE
The following test procedure is outlined as a minimum effort to ensure correct modem
operation. It relies on a diagnostic capability of the modem called analog loopback in
which the modem communicates with itself. More thorough testing requires highly
specialized equipment and is beyond the scope of this document.
EQUIPMENT REQUIRED
1. Dumb terminal or computer with terminal emulation software.
2. Cable to interface terminal to modem. (DB-9S to DB25S)
3. 170 traffic controller with no cards installed.
4. Access to standard dial-up telephone line.
PREPARATION
1. Configure terminal device for 1200 baud, 7 data bits, 2 stop bits and even parity.
2. Connect interface cable between the terminal and J14.
3. Connect phone line to RJ11 jack "LINE".
4. Install modem in modem slot of controller.
5. Power up terminal.
BEGIN TEST
1. Power up controller observing LED's on front edge of modem. After modem
initialization, lamps labeled AA and DCD should be on. (If not, see Shipping
Configuration.)
2. Enter ATS18=0&T1 <return> on the terminal. This enables the Local Analog
Loopback mode.
3. The modem is now essentially connected to itself. Characters typed at the
keyboard are sent through modulator and demodulator sections of the modem and
returned to the terminal. Therefore characters seen at the terminal should be exactly those
typed. Type a message with many different characters such as "the quick brown fox jumps
over the lazy dog". Verify that what is seen on the screen is exactly what was typed.
Verify that, while typing, the TXD and RXD lamps flash.
4. Type +++ <no return>. This should cause the modem to respond with "OK" and
return to command mode.
5. Enter AT&T0 <return> ending the test. Modem should respond "OK".
6. Call the modem from a remote phone. The modem should answer the call (OH
light on), respond with "RING" on the terminal, and you should hear a tone. After around
30 seconds the modem should hang up (OH light off) and respond "NO CARRIER".
7. Type ATDPn <return> where n is the phone number of the remote phone. The
modem should go off hook and pulse dial the number. The remote phone should ring.
Answer it! It's for you. You should hear nothing on the phone, but after around 30 seconds
the modem will hang up and respond "NO CARRIER".
END OF TEST

COMMAND SET
The call set-up and user option commands for the Model SM2400 are designed to be
compatible with the Hayes Smartmodem 2400. The following paragraphs explain the
functional groups and the function of each of the user options. One configuration option is
assigned a switch setting and is referred to as an 'adjustment'. These options will configure
the modem for the basic operating modes. The software commands can be issued from an
ASCII terminal in serial mode, or from a microcomputer through a DART or USART.
These commands allow the user to personalize the modem to his or her environment. Nine
of the twenty-seven commands can be saved in a non-volatile RAM.
SOFTWARE CONFIGURATION COMMANDS
This section lists all the Model SM2400 codes, commands and registers, that may be used
while configuring the modem. Commands instruct the modem to perform an action, the
value in the associated registers determine how the commands are performed, the result
codes returned by the modem tell the user about the execution of the commands.
The following paragraphs arrange the codes into functional groups. The commands are of
four basic types, dialing, answering, standard functions, and special functions.
The commands can be entered in a string, with or without spaces, any spaces within or
between commands will be ignored by the modem. During the entry of any command, the
"delete" or "backspace" key can be used to correct any error. Upper case or lower case
characters can be used in the commands. Some exceptions to this rule are mentioned in
association with the specific commands.
All the commands described in the following paragraphs refer to asynchronous terminals
using ASCII codes.
(AT) Attention Code
The attention code, ‘AT’, begins every command line except A/. AT may be entered as
upper or lower case characters, and cannot be deleted using backspace or delete keys.
More than one command can be placed on a single line and separated with spaces for
readability. The command line must end with the ASCII character stored in S Register 3,
which defaults to decimal 13 (Carriage Return). A line with no carriage return will be
ignored. Commands following the AT are processed after receiving the carriage
return character. This attention code is used by the modem to detect the bit rate and
character format of the connected DTE.
(A) Answer Command
This command causes the modem to go off-hook and take control of the telephone line (in
answer mode), from the telephone set. After receiving this command the modem cannot
accept any more commands, as it immediately answers the call and goes into the data
transmission mode. While in the data mode the Escape code (+++) will return the modem
to the command mode.

(A/) Repeat Command
AT does not precede this command. The repeat command instructs the modem to repeat
the execution of the last command line stored in the command buffer. The repeat
command can be used to redial a number if busy. This command is neither followed by
carriage return, nor preceded by the attention command AT. THE COMMAND BUFFER
IS LOST AFTER A CONNECTION IS MADE. While the modem is connected, the
'escape state' command buffer is purged. This causes the last number dialed to be lost.
(Bn) BELL/V.24 Protocol Compatibility
The B command selects the protocol for 1200 and 300 bps operation. This command
selects the mode of the data set, between CCITT and Bell modes. The command is
ignored when the modem operation is at 2400 bps. BO sets the modem to CCITT modes
V.22 bis (1200 bps) and V.21 (300 bps). The default B1 sets the modem to Bell modes
212A (1200 bps) and 103 (300 bps).
CCITT mode V.22 bis sends 2100 Hz for 3.3 seconds and 75 mS of silence followed by
unscrambled ones in the answer mode, while the BELL 212A protocol simply sends 2225
Hz.
The transmitted signal in the originate mode sends scrambled ones at 1200 bps for both
V.22 bis and Bell 212A.
(Dstring) The Dialing Commands
The Dstring command causes the modem to go to the auto-dial mode in switched line, or
to originate a call in leased line. The parameters for 'string' include S=n(stored string),
digits 0 to 9, touch-tones A to D, *, #, the period and slash, P, R, T, comma and
semicolon. Punctuations (parenthesis, hyphen, and spaces) entered for readability are
ignored. Modifiers are described below.
P,T These commands select between the pulse and tone dialing for the succeeding
digits to be dialed. With either P or T type dialing command, the dialing begins
after the timeout period defined by register S6.
, The comma causes the modem, while dialing, to pause for the time specified by
register S8 (default is 2 seconds). This parameter is used for example, to pause
between dialing an external access code from a PBX, and then dialing the
desired number.
; The semicolon placed at the end of a dial command places the modem in
command state after dialing. It does not provide connection with another modem,
but holds the line for further commands. The modem asserts that it has finished
dialing by returning the result code `OK'. This command is useful in dialing long
numbers.

@ The @ command causes the modem to wait for the time specified by register S7
for one or more rings, followed by 5 seconds of silence before going to the next
symbol in the dialing string. S7 default is 30 seconds.
! The flash command causes the modem to go on-hook for 1/2 second. Flash might
be used for transferring calls.
S,S=n Dial string stored in NVRAM (See &Zn=string). ATDS will dial stored string O.
ATDS=n will dial stored string n where n is 0 through 3.
R The Reverse command at the end of dialing permits the establishment of a call in
reverse mode, i.e., the local modem, which originated the call enters the "answer'
mode. This would be a useful command for communicating with an `originate
only' modem at a remote site.
W Causes modem to wait for a dial tone while dialing.
(En) Echo Command
The Echo command determines whether the modem will echo the characters sent to it
while in the command state. E1 causes the modem to echo, which is the system default,
and EO sets the modem to no echo.
(Hn) Switch Hook Control
The H or HO (default) command will cause the telephone line relay to disconnect (hang
up). The H1 command will cause the telephone line relay to go off-hook.
(In) Request Product Code and Checksum
The I command requests the product code. The Model SM2400 will respond with 24x
where x is the software revision level. The command Ii will cause a checksum to be
computed on the internal ROM and returned as three ASCII numeric characters followed
by a carriage return, line feed. The 12 command returns a computed checksum with a
response of OK or ERROR.
(Ln) Speaker Volume
L,L0,L1 Low Volume
L2 Medium Volume (default)
L3 High Volume
Example: ATL3 (Sets the speaker volume to high)

(Mn) Monitor On/Off
M speaker is off MO speaker is off
M1 speaker is off while receiving carrier (default)
M2 speaker always on
M3 speaker disabled while dialing or receiving carrier
(On) On-Line
The 0 command is used to return the modem to the on-line mode, after temporarily
bringing it to the command mode by using the escape code (+++). 01 will cause the
modem to return to the online state and initiate a retrain sequence (2400 bps only). Issuing
an ATO from an off-line idle state will evoke a "NO CARRIER" response. ATO issued
from the call progress mode (after an "ATDxxxxx;" which puts the modem in a command
state after dialing) causes the modem to remain in the originate mode.
(Qn) Result Codes
The Q command turns on and off result codes during execution of commands. The code
QO (default) enables the result codes to be sent. When set to Ql, the modem will not
return result codes. S register values, identification codes, checksum results, and results of
test modes with self tests are returned.
(Sr) Direct Register Commands
Sr? Returns current decimal value of S register r.
Sr=n Writes the 8 bit binary equivalent of n (0-255 decimal) to S register r.
Modem configuration variables are kept in 8 bit storage elements called "S registers".
Some registers are dedicated to one function while others share the 8 bits to store
information about the status of different commands (bit mapped). For an intelligent 'Host',
it may be easier to directly write the desired data into the S registers rather than going
through the longer process of stepping through each command. Understanding these
registers allows the user to configure the modem at any time, and to change only the
desired parameters.
(Vn) Verbal/Numeric (Verbose/Terse)
The Vn command selects the type of result codes returned by the modem after or during
the execution of commands. V1 selects word result codes (default). VO selects digit result
codes.

Result Codes Returned by Modem
Meaning Short Form Long Form
Command Line Executed Without Errors 0 OK
Connected at 300 bps 1 CONNECT
Local Telephone Line Ringing 2 RING
Carrier Lost or Never Received 3 NO CARRIER
Error in Command Line 4 ERROR
Invalid Command Line
Line Length Exceeds Buffer Size
Invalid Character Format
Connected at 1200 bps 5 CONNECT 1200
No Dial Tone Received Within Time-Out 6 NO DIAL TONE
Called Line Busy 7 BUSY
No Answer Within Time-Out 8 NO ANSWER
Connected at 2400 bps 10 CONNECT 2400
Long form results are preceded and terminated with both carriage return and line feed
characters. Short form codes are only terminated with a carriage return.

(Xn) Enable Extended Result Code
Forms of this command can have an effect on Long Form CONNECT messages, Dialing
(Blind or Wait for Dial Tone), and BUSY detection. 'Blind' dialing means that the modem
goes off-hook and waits a time period specified by register S6 before dialing regardless of
the presence or absence of dialtone. Wait for Dial Tone dialing means that the modem
goes off hook and waits the time period specified by register S6 to receive a dial tone
before dialing. If no dial tone is received within the allotted time, the modem returns NO
DIAL TONE.
X or XO Connect Message - CONNECT
Dialing - Blind (set S6 before dial)
Dial Tone Timeout - No
Busy Detection - No
X1 Connect Message - Full Message
Dialing - Blind Dial Tone Timeout - No
Busy Detection - No
X2 Connect Message - Full Message
Dialing - Waits for Dial Tone
Dial Tone Timeout - Yes (5 seconds fixed)
Busy Detection - No
X3 Connect Message - Full Message
Dialing - Blind
Dial Tone Timeout - No
Busy Detection - Yes (modem will return BUSY)
X4 (default) Connect Message - Full Message
Dialing - Waits for Dial Tone
Dial Tone Timeout - Yes (S6)
Busy Detection - Yes
(Yn) Enable Long Space Disconnect
Y or YO (default) disables this option. Yl sets the modem to disconnect when a space of
1.6 seconds or more is received from the remote modem. Also, under Yl, a space of 4
seconds is sent prior to going on-hook upon receiving a HO command or detecting an ON
to OFF transition on DTR if &D option is selected.
(Zn) The Reset Command
This command causes a reset and a recall of the profile that was saved in NVRAM by the
&Wn command and then returns 'OK'.
Valid forms: ATZ or ATZO - recalls profile 0 (same as power up)
ATZ1 - recalls profile 1
Any subsequent characters in the command line will be ignored.

(+++) The Escape Code
The escape code returns the modem to the command state from the online state, without
releasing the telephone line. This command consists of an escape guard time (S12 default
1 second) and an escape character (ASCII code in S2 default '+'). The escape character
must be issued three consecutive times with a guard time before and after the characters.
If the sequence is successful, the modem responds 'OK' and enters an 'escape' command
state.
(&Cn) DCD Options
&C or &CO maintains a DCD ON condition and ignores the actual state of the data
carrier from the remote modem. &C1 (default) causes DCD to reflect remote carrier
status.
(&Dn) DTR Options
&D or &DO causes the modem to ignore DTR. After the &D1 command the modem will
go from data mode to command state on an ON to OFF transition of DTR. For &D2
(default) an ON to OFF transition of DTR will cause the modem to go on-hook, disable
auto-answer, and end in the command state. &D3 causes the modem to reset (see Zn
command) if it detects an ON to OFF transition of DTR. DTR transitions during idle state
will not generate any result codes or have any other effect on the modem.
- Any ON to OFF state change in DTR must last longer than the period specified by S25
in order to be recognized.