CyberResearch RS-232 User manual

Serial Communications
USER’S MANUAL
VER. D • OCT 2001
No part of this manual may be reproduced without permission
COMT 366 Series
RS-232 to RS-485 Converter
with LCD, 38.4 kbps Data Rate
COMT 366M: DB-25M Connector
COMT 366F: DB-25F Connector
®
CyberResearch®,Inc.
www.cyberresearch.com
25 Business Park Dr., Branford, CT 06405 USA
203-483-8815 (9am to 5pm EST) FAX: [phone]

CyberResearch® Serial Communications COMT 366 Series
CyberResearch, Inc. iii
25 Business Park Drive P: [phone]; F: [phone]
Branford, CT USA www.cyberresearch.com
©Copyright 2001
All Rights Reserved.
October 15, 2001
The information in this document is subject to change without prior notice
in order to improve reliability, design, and function and does not represent
a commitment on the part of CyberResearch, Inc.
In no event will CyberResearch, Inc. be liable for direct, indirect, special,
incidental, or consequential damages arising out of the use of or inability
to use the product or documentation, even if advised of the possibility of
such damages.
This document contains proprietary information protected by copyright.
All rights are reserved. No part of this manual may be reproduced by any
mechanical, electronic, or other means in any form without prior written
permission of CyberResearch, Inc.
Trademarks
“CyberResearch,” and “COMT 366 Series,” are trademarks of
CyberResearch, Inc. Other product names mentioned herein are used for
identification purposes only and may be trademarks and/or registered
trademarks of their respective companies.
• NOTICE •
CyberResearch, Inc. does not authorize any CyberResearch product for
use in life support systems, medical equipment, and/or medical devices
without the written approval of the President of CyberResearch, Inc. Life
support devices and systems are devices or systems which are intended
for surgical implantation into the body, or to support or sustain life and
whose failure to perform can be reasonably expected to result in injury.
Other medical equipment includes devices used for monitoring, data
acquisition, modification, or notification purposes in relation to life
support, life sustaining, or vital statistic recording. CyberResearch
products are not designed with the components required, are not subject
to the testing required, and are not submitted to the certification required
to ensure a level of reliability appropriate for the treatment and diagnosis of
humans.

COMT 366 Series CyberResearch® Serial Communications
iv ©Copyright 2001 CyberResearch, Inc.
COMT 366 Series

CyberResearch® Serial Communications COMT 366 Series
CyberResearch, Inc. v
25 Business Park Drive P: [phone]; F: [phone]
Branford, CT USA www.cyberresearch.com
FCC Information
WARNING: This equipment generates, uses, and can radiate radio frequency energy and
if not installed and used in accordance with the instruction manual, may cause
interference to radio communications. It has been tested and found to comply with the
limits for class A computing devices pursuant to Subpart B of Part 15 of FCC Rules,
which are designed to provide reasonable protection against such interference when
operated in a commercial environment. Operation of this equipment in a residential area
is likely to cause interference. If this occurs, the user will be required to take whatever
measures may be required to correct the interference at his own expense.
Certificate Of FCC Compliance for Canada
This digital apparatus does not exceed the Class A limits for radio noise emissions from
digital apparatus set out in the Radio Interference Regulations of the Canadian
Department of Communications.
Le present appareil numerique n'emet pas de bruits radioelectriques depassant les limites
applicables aux appareils numeriques de la classe A prescrites dens le Reglement sur le
brouillage radioelectrique edicte par le ministere des Communications du Canada.

COMT 366 Series CyberResearch® Serial Communications
vi ©Copyright 2001 CyberResearch, Inc.
1.0 General Description ............................ 1
1.1 The LCD.................................................................................... 1
2.0 Specifications ....................................... 3
2.1 Interface ................................................................................... 3
2.2 Connectors .............................................................................. 3
2.3 Data Rate.................................................................................. 3
2.4 Switches................................................................................... 3
2.5 Indicators ................................................................................. 3
2.6 Power........................................................................................ 3
2.7 Size ........................................................................................... 3
2.8 Environment ............................................................................ 3
3.0 Installation ........................................... 4
4.0 Operation ............................................. 5
4.1 Termination of the Line........................................................... 6
5.0 Troubleshooting................................... 7
6.0 RS-232 Pin Number Assignments...... 9
7.0 Power.................................................. 10
7.1 COMT 366............................................................................... 10

CyberResearch® Serial Communications COMT 366 Series
CyberResearch, Inc. 1
25 Business Park Drive P: [phone]; F: [phone]
Branford, CT USA www.cyberresearch.com
1.0 General Description
The COMT 366 converter provides a convenient method of interfacing EIA-232-based
equipment with an RS-485 network using a half-duplex, single twisted-pair transmission
protocol. The COMT 366 provides the capability for a high-speed, low cost, local area
network. Up to 32 users can be supported at rates up to 38.4K Baud and total separations
of 6,000 feet. The LCD feature assists with installation and troubleshooting.
1.1 The LCD
Your COMT 366 product incorporates an LCD display designed to provide meaningful
information to the user. It will assist in the initial installation and check out; thereafter it
can be used as a performance monitor. In the case of a system problem, it provides
information as to the status of the local link.
The logo shown on the LCD display indicates the unit is powered. For power-stealing
devices such as a converter, it is an indication that sufficient power is being applied to
operate the device. The LCD display uses less than 1 milliWatt of power.
The data display on the LCD consists of graphical representations of TD (Transmit Data)
and RD (Receive Data). Each of these signals is displayed the way a bit-change
waveform would appear on an oscilloscope. Ordinarily, TD and RD are low or a minus
voltage in the quiescent state. When data is transmitted, the transmit signal is brought
high to a positive voltage. These two signal states are displayed on the LCD by either a
low segment or a high segment. The low segment represents the minus voltage (the mark
condition) while the upper segment represents a positive voltage (the space condition).
The vertical bar connecting the lower segment to the upper segment is always on when
power is applied.

COMT 366 Series CyberResearch® Serial Communications
2 ©Copyright 2001 CyberResearch, Inc.
If the transmit signal is in the quiescent state (continuously low) only the lower segments
and the vertical bar will be illuminated. This indicates a constant negative state. If the
transmit or receive inputs to the device were streaming, i.e., in the positive mode
continuously, the LCD display would show the vertical segment and the upper segments
only. For those cases where there is valid data transmission, both the upper and lower
segments will be displayed simultaneously. A variation in display intensity between
lower and upper segments will give the user a perception of the amount of data being
transmitted.
The LCD display also shows the status of the following control signals: CTS, RTS, DSR,
DCD, and DTR. These signals are displayed as mnemonic symbols, composed of three
letters each, on the bottom line of the display. The presence of the three-letter mnemonic
indicates that the respective control signal is high or positive. If the control signal is
negative, the three-letter mnemonic is not displayed. For most full-duplex data-only
converters, CTS and RTS are connected together while DSR, DCD, and DTR are
connected together. The LCD display will help verify correct operation.

CyberResearch® Serial Communications COMT 366 Series
CyberResearch, Inc. 3
25 Business Park Drive P: [phone]; F: [phone]
Branford, CT USA www.cyberresearch.com
2.0 Specifications
2.1 Interface
Conforms to EIA RS-232 and RS-485 specifications.
2.2 Connectors
Five-position terminal block.
2.3 Data Rate
0 to 38.4 KBPS
2.4 Switches
DTE/DCE selector switch: allows reversing of Pins 2 and 3 of EIA-232 connector.
Four-position dip switch: two switches set operating mode, two switches set cable
termination value.
2.5 Indicators
Equipped with an LCD display for data, five control signals and power.
2.6 Power
115VAC @ 60 Hz (220 VAC @ 50 Hz optional).
2.7 Size
COMT 366 : 2" W x 4.15" L x 0.79" H (50.8mm x 105.4mm x 20.1mm)
2.8 Environment
0oto 50oC, 5% to 95% relative humidity.

COMT 366 Series CyberResearch® Serial Communications
4 ©Copyright 2001 CyberResearch, Inc.
3.0 Installation
The COMT 366 is designed to interface EIA-232 with RS-485 equipment. The EIA-232
device can be either a DTE or DCE type device. The DTE/DCE selector switch allows
for reversing Pins 2 and 3 ( TD and RD), thereby eliminating the need for null modem
cables. If the switch is in the DTE position, Pin 2 of the RS-232 connector is an output
for the COMT 366.
The half-duplex nature of RS-485 allows for a Master-Slave configuration. In a network,
the master will poll the slaves through the single twisted pair and request that only one
device access the line at a time.
The COMT 366 can operate at the following Baud rate/distance combinations:
Baud rate: 38.4 K 19.2K 9.6K and below
Distance (ft.) 4000 6000 18000
Two pairs of screw terminals are provided to allow the pass through of the twisted pair.
This simplifies installation of a network. There are internal connections between both
positive and both negative terminals.
The COMT 366 can be interfaced to the network bus in two configurations. However, the
results of both configurations are identical. The first configuration allows for a direct
splice into the bus. The second configuration creates a "T" at the bus and runs a stub of
wire to the unit.

CyberResearch® Serial Communications COMT 366 Series
CyberResearch, Inc. 5
25 Business Park Drive P: [phone]; F: [phone]
Branford, CT USA www.cyberresearch.com
4.0 Operation
Operation in an RS-485 environment requires all devices attached to the network to have
some level of intelligence in order to establish an orderly flow of data on the single
twisted pair. The COMT 366 offers three possibilities for hardware data flow control.
The user selects the mode which avoids the contention problem. Unless contention is
resolved, there is the possible collision of data caused by two devices attempting to
transmit simultaneously. The software control is the responsibility of the user.
The RTS (Pin 4) and CTS (Pin 5) signals of the EIA-232 connector are jumpered
together. This combined signal (referred to as RTS) is used to control the transmitter and,
depending on the mode, can also control the receiver. The COMT 366 can only transmit
data on the RS-485 port if RTS is asserted.
Note: On the COMT 366 only: if the RTS signal cannot be controlled, then carefully
open the covers and locate JP1 and move the jumper to the adjacent pin. This allows the
TD signal to control the transmitter.
Positions 3 and 4 of the dipswitch control the I/O circuits of the RS-485 port as indicated
below:
Mode 3 4 Transmitter Receiver
1 Off Off Controlled by RTS Disabled
2 On Off Controlled by RTS Enabled when no
RTS
3 Off On Controlled by RTS Enabled
4 On On Disabled Enabled
An analysis of the operating modes reveals that Mode 2 or 3 are the most useful in the
majority of installations. Mode 3 allows the converter to "listen" to the line at all times,
including its own transmission. This allows observation of data collisions if they occur.
The RTS indicator displays the status of the RTS/CTS signal applied to the control ports
of the RS-485 transmitter and receiver as set by the Mode switches. Mode 4 disables the
transmitter completely, regardless of the RTS/CTS signal; the RTS display reflects the
disabled status.

COMT 366 Series CyberResearch® Serial Communications
6 ©Copyright 2001 CyberResearch, Inc.
4.1 Termination of the Line
There are four user-selectable resistive terminating values which are implemented using
switches A and B of the dipswitch. As the length of the transmission cable and the
number of users increases, the chosen value becomes more critical to error-free operation.
Typically, devices at the end of a long bus are terminated and units multi-dropped
between the ends are not terminated. The cable used to connect devices off the long bus
should be kept as short as possible. The value chosen should match the characteristic
impedance of the twisted pair being used. The termination value can be selected using the
following table
Switch Termination Value
1 2 OHMS
Off Off None
On Off 200
Off On 120
On On 75

CyberResearch® Serial Communications COMT 366 Series
CyberResearch, Inc. 7
25 Business Park Drive P: [phone]; F: [phone]
Branford, CT USA www.cyberresearch.com
5.0 Troubleshooting
The following is a list of possible problems that may arise during the installation and
solutions to those problems:
1. The data being received is garbled.
a) The DTE/DCE switch is not set properly (see Section 3.0, "Installation"). On the
COMT 366, observe the LCD and verify that TD and RD are shown as low in the
quiescent state (see Section 1.1, "The LCD").
b) The equipment that the COMT 366 is connected to does not have the communication
parameters set the same.
On the COMT 366 look at the LCD, if RD is shown as a constant high or streaming (see
Section 1.1, The LCD") then the wires are reversed.
d) One of the two wires is broken.
2. No data is being received.
a) Customer equipment not connected
b) The DTE/DCE switches are not set properly (see Section 3.0, "Installation").
c) One or more wires between the modems are open.
d) Link connection exceeds maximum specified distance. Individual converter
performance can be verified if the device to which the converter is connected is capable
of full-duplex operation. A standard CRT terminal is ideal for this test. In this mode the
terminal will generate data from its keyboard and be transmitted via Pin 2. However, data
will not be displayed until it is received at its input port, Pin 3.

COMT 366 Series CyberResearch® Serial Communications
8 ©Copyright 2001 CyberResearch, Inc.
The converter may now be tested by setting the following switches:
DCE on COMT 366
DTE
Dip Switch
1 ON
2 OFF
3 OFF
4 ON
If the converter is functioning correctly, any data entered on the keyboard of the terminal
should appear on the screen and the TD and RD indicators should flash indicating the
flow of data.

CyberResearch® Serial Communications COMT 366 Series
CyberResearch, Inc. 9
25 Business Park Drive P: [phone]; F: [phone]
Branford, CT USA www.cyberresearch.com
6.0 RS-232 Pin Number Assignments
Pin EIA CCITT Name
2 BA 103 Transmit Data *
3 BB 104 Receive Data *
4 CA 105 Request to Send **
5 CB 106 Clear to Send **
6 CC 107 Data Set Ready ***
7 AB 102 Signal Ground Gnd
8 CF 109 Data Carrier Detect ***
20 CD 108.2 Data Terminal Ready ***
* These signals can be reversed using the selector switch.
**, *** Connected together

COMT 366 Series CyberResearch® Serial Communications
10 ©Copyright 2001 CyberResearch, Inc.
7.0 Power
The COMT 366 can be either host or self powered. In the self-powered mode, a wall-
mounted transformer supplies low voltage AC and the required +12, -12, and +5 Volts
are generated internally. For COMT 366, supply +12 volts on Pin 9.
7.1 COMT 366
The COMT 366 is powered by a small, wall-mounted transformer that supplies 12 VDC
@ 500 mA. The transformer must be connected to the COMT 366 through the 1.3mm
connector located on the side of the unit before plugging the transformer into the wall.

CyberResearch® Serial Communications COMT 366 Series
CyberResearch, Inc. 11
25 Business Park Drive P: [phone]; F: [phone]
Branford, CT USA www.cyberresearch.com
Product Service
Diagnosis and Debug
CyberResearch, Inc. maintains technical support lines staffed by experienced
Applications Engineers and Technicians. There is no charge to call and we will
return your call promptly if it is received while our lines are busy. Most problems
encountered with data acquisition products can be solved over the phone. Signal
connections and programming are the two most common sources of difficulty.
CyberResearch support personnel can help you solve these problems, especially
if you are prepared for the call.
To ensure your call’s overall success and expediency:
1) Have the phone close to the PC so you can conveniently and quickly take
action that the Applications Engineer might suggest.
2) Be prepared to open your PC, remove boards, report back-switch or
jumper settings, and possibly change settings before reinstalling the
modules.
3) Have a volt meter handy to take measurements of the signals you are
trying to measure as well as the signals on the board, module, or power
supply.
4) Isolate problem areas that are not working as you expected.
5) Have the source code to the program you are having trouble with available
so that preceding and prerequisite modes can be referenced and
discussed.
6) Have the manual at hand. Also have the product’s utility disks and any
other relevant disks nearby so programs and version numbers can be
checked.
Preparation will facilitate the diagnosis procedure, save you time, and avoid
repeated calls. Here are a few preliminary actions you can take before you call
which may solve some of the more common problems:
1) Check the PC-bus power and any power supply signals.
2) Check the voltage level of the signal between SIGNAL HIGH and SIGNAL
LOW, or SIGNAL+ and SIGNAL– . It CANNOT exceed the full scale range
of the board.
3) Check the other boards in your PC or modules on the network for address
and interrupt conflicts.
4) Refer to the example programs as a baseline for comparing code.

COMT 366 Series CyberResearch® Serial Communications
12 ©Copyright 2001 CyberResearch, Inc.
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