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1994-03-23
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D L M
An IBM P.C. Based
RS-232 Asynchronous
Data Line Monitor
Release 1.4
Revised 04-Jan-94
Copyright 1989-1994 Dave Dunfield
All rights reserved
Data Line Monitor Page: 1
1. INTRODUCTION
Have you ever been in the situation where you have two serial
devices (such as a PC and a printer), which SHOULD work but just
don't seem to communicate? Or perhaps you are trying to debug a new
communications protocol, and when you start the file transfer
evrything just LOCKS UP!!!
In such situations, wouldn't it be nice to be able to SEE exactly
what is happening over the RS-232 cable? To SEE when characters were
received in relation to characters going out? To SEE flow control
characters and their effect? To SEE the modem carrier drop?
Wouldn't it be nice to do all this WITHOUT spending $5,000 -
$10,000 on a commercial data scope?
If your requirements are simple monitoring of ASYNCHRONOUS RS-232
serial communications, DLM (Data Line Monitor) is for you!!!
The DLM "package" (software and documentation) is copyrighted, and
may not be re-distributed for profit or other commercial purposes
without my written permission. If you find DLM useful, please help me
continue to support and enhance it by sending a "registration" fee
(specified in the included CATALOG file) to this address:
Dunfield Development Systems
P.O. Box 31044
Nepean, Ontario (Canada)
K2B 8S8
Please make your cheque or money order payable to "Dunfield
Development Systems". If you choose not to order the complete DLM
package, please discontinue using DLM within thirty days.
Registered users will receive (in addition to the latest copy of
DLM), supplementary utilities, including an "error generator" for
inserting errors in data transmission lines, a VT-100 terminal
checkout program, a "pop-up" (TSR) ANSI terminal, and more.
DLM is provided on an "as is" basis, with no warranty of any kind.
In no event shall the author be liable for any damages arising from
its use or distribution.
Data Line Monitor Page: 2
1.1 What is DLM?
DLM is an easy to use DATA LINE MONITOR for use on the IBM P.C.
It displays DTE and DCE data in a split line format (DTE over
DCE), and records up to 32767 events (characters and/or signal
transitions) in a circular buffer for later review (If the buffer
overflows, the LAST 32767 events are available).
Recorded data may be saved to disk, allowing a problem to be
captured in the field, and the results viewed at another time and
place. Since the data is stored as a standard DOS file, it may be
transmitted over a modem and viewed (using DLM) at a remote
location. This allows an engineer at the main office to provide
better (and faster) support to a technician in the field, since he
can also SEE the problem.
It supports ASYNCHRONOUS operation at 110, 300, 1200, 2400,
4800, 9600 and 19200 BPS; 5,6,7 and 8 data bits; Even, Odd, Mark,
Space and No parity; and 1 or 2 stop bits. The DTE configuration
may be set independantly of the DCE configuration for split
speed/format operation.
The configuration may also be saved to disk, allowing you to
have several "canned" setups for common situations.
In addition to the data line monitor, DLM incorporates a SIGNAL
MONITOR (LIGHT BOX) for real time monitoring of the hardware
signals.
1.2 Hardware Required
All that is required to use DLM is an IBM P.C. (or compatible)
which has two serial (COMM) ports. A special "Y" adapter cable
(described later) must be constructed to allow monitoring of both
DTE and DCE data.
Data Line Monitor Page: 3
2. HARDWARE SETUP
Before you use DLM, you must construct a special "Y" adapter cable
which allows it to monitor "both sides" (DTE and DCE) of a single
communications line using the IBM P.C. serial ports (COM1 and COM2).
2.1 IBM P.C. serial ports
The serial ports of the IBM P.C. are RS-232 DTE configuration,
and will be in either a 25 or 9 pin configuration. The ports have
the following pinout:
Signal name Origin 25-Pin(PC) 9-Pin(AT)
---------------------------------------------------------
Transmit Data (TXD) DTE 2 3
Receive Data (RXD) DCE 3 2
Request To Send (RTS) DTE 4 7
Clear To Send (CTS) DCE 5 8
Data Set Ready (DSR) DCE 6 6
Signal Ground (GND) --- 7 5
Data Carrier Detect (DCD) DCE* 8 1
Data Terminal Ready (DTR) DTE 20 4
Ring Indicator (RI ) DCE 22 9
* In order to be able to record this signal in data capture
mode, DLM records it as if it were originated by the DTE.
Note that since the PC serial port is a DTE, it drives the
signals with DTE origin, and monitors the signals with DCE origin.
Therefore, all connections to the line being monitored will be to
the DCE signals of the COMM port.
Data Line Monitor Page: 4
2.2 Passive Monitor Cable
DLM monitors DTE data on COM1, and DCE data on COM2. Therefore,
you must connect the input (DCE) lines from COM1 to the DTE origin
signals on the monitored line, and the input (DCE) lines from COM2
to the DCE origin signals.
To do this, you must construct a "Y" adapter cable, which
contains a set of "straight through" connectors which are inserted
in the RS-232 line being monitored, and also connects the DTE and
DCE signals to the appropriate input (DCE) pins on COM1 and COM2.
Be sure to mark which COMM port each of the two "PC" connectors
connects to. If you get them backwards, the DTE/DCE data and
signals will appear reversed.
"Straight through" "IBM PC"
Line Monitor Connector COMM port connectors
DB-25 Male /----- COM1 (Monitor DTE)
| | | | | | | /
+-+-+-+-+-+-+==================<
| | | | | | | \
DB-25 Female \----- COM2 (Monitor DCE)
The signals must be connected as follows:
Line Pin Port 25-Pin(PC) 9-Pin(AT)
-------------------------------------------------
TXD 2 ---- COM1 3 2