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Text File | 1990-11-26 | 25.8 KB | 583 lines

D L M An IBM P.C. Based RS-232 Asynchronous Data Line Monitor Release 1.2 Revised 15-Aug-90 Copyright 1989,1990 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 of $15 to this address: Dave Dunfield 56 Burnetts Grove Circle, Nepean, Ont. (Canada) K2J 1N6 Users ordering the update disk at the time of registration 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 RXD 3 ---- COM2 3 2 RTS 4 ---- COM1 5 8 CTS 5 ---- COM2 5 8 DSR 6 ---- COM2 6 6 GND 7 ---- COM1+COM2 7 5 DCD 8 ---- COM1 22 9 DTR 20 ---- COM1 6 6 RI 22 ---- COM2 22 9 Aux 1* - ---- COM1 8 1 Aux 2* - ---- COM2 8 1 * These signals will be shown in "signal monitor" function, but will not be recorded in "data capture" function. You may use them to monitor any signals you like. Data Line Monitor Page: 5 3. USING DLM To set up DLM, connect the "straight through" end of the "Y" adapter cable to the line to be monitored, and the "PC" connectors to the appropriate COMM ports on the IBM P.C. Execute DLM from the DOS command line, and you will be greeted with The following menu: +-------------------------+ | Begin data capture | | Review captured data | | Clear capture buffer | | RS-232 Signal monitor | | Serial port parameters | | Disk transfer functions | | Exit to DOS | +-------------------------+ Each of the above menu items is described below: 3.1 Begin data capture This option causes DLM to begin monitoring the data line. Any data or signal transitions detected are displayed in a "split line" screen format (in real time), as well as recorded in the circular capture buffer. Each set of lines on the screen (DTE/DCE data) has a dashed "separating" line, DTE data will appear ABOVE the line, and DCE data will appear BELOW the line. A cursor is displayed ON the dashed line to indicate where the next data item will be displayed. Signal transitions and line errors are displayed as an "arrow" which points UP if the event was from the DTE, and DOWN if the event was from the DCE. One exception to this is the DCD signal which occurs from the DCE, but is recorded by DLM as if it were from the DTE. This is because each "direction" (DTE/DCE) may only have three (3) signals recorded in the capture buffer. The DCE signals are DSR, CTS and RI; The DTE signals are DTR, RTS and DCD. The exact signal or error occuring may be displayed in "Review captured data". Press ESCAPE at any time to exit this function, and return to the main menu. Data Line Monitor Page: 6 3.2 Review captured data In this function, the same "split line" screen as above is displayed, however it shows data previously captured. The ARROW keys may be used to move the cursor around the display. The PGUP and PGDN keys may be used to advance and backup by entire screens. The HOME key returns you to the beginning of the buffer. When the cursor is positioned over an entry, it will contain a "arrow" ('^' or 'v') which indicates the origin (DTE or DCE) of that entry (In most cases it will be obvious since data will be shown above or below the line). The hex value of any data will be shown near the center of the status line at the top of the screen. To the immediate right the four "data" flags will be shown: F - Framing error P - Parity error O - Overrun error D - Data is present To the right of that, three signals will be shown: DTE DCE --------- --------- X - DCD X - RI T - DTR S - DSR R - RTS C - CTS At the extreme right side of the status line will be shown two numbers. The first is the current position in the capture buffer, and the second is the total number of entries in the capture buffer. Press ESCAPE at any time to exit this function, and return to the main menu. 3.3 Clear capture buffer This function removes any data which has been previously recorded from the "capture" buffer. It is useful to remove old data before starting a new monitoring session, otherwise any new data will be appended to the old data already in the buffer. When you execute this function, DLM displays the number of entries currently residing in the capture buffer. Press ENTER to clear the buffer, or ESCAPE to exit and leave it unchanged. Data Line Monitor Page: 7 3.4 RS-232 Signal monitor This function provides a "light-box", which shows all of the hardware signals being monitored (DTR, DSR, RTS, CTS, DCD, RI, AS1 and AS2). Each signal has a "light" which will be ON (white) if the signal is asserted, and OFF (dark) if the signal is not asserted. Changes occuring in the signal states are shown in "real-time", so that the display always reflects the actual state of the line signals. Press ESCAPE at any time to exit this function, and return to the main menu. 3.5 Serial port parameters This function allows you to set the speed and data format of the ports monitoring DTE and DCE data. In order for DLM to correctly monitor the data line, these parameters must be set up the same as the devices being monitored. A sub-menu is provided which allows you to set both the DTE and DCE parameters simultaneously, or individually. Most modern serial communications operate the DTE and DCE at the same speed and format. Press ESCAPE at any time to exit each menu level, and return to the next higher menu. 3.6 Disk transfer functions This function provides you with a sub-menu, which allows you to load/save configuration or captured data to/from disk files: +--------------------+ | Load Data Image | | Load Configuration | | Save Data Image | | Save Configuration | +--------------------+ Once you select a transfer operation, you will be prompted for a file name. The following special keys may be used: Left arrow - Move to left Right arrow - Move to right Home - Move to beginning of name End - Move to end of name PgUp - Clear entire field PgDn - Clear from cursor to end of field ESC - Cancel and return to higher menu ENTER - Accept filename & perform operation Data Line Monitor Page: 8 3.7 Exit to DOS This function terminates DLM, and returns to the DOS command prompt. 4. DEBUGGING TIPS Here are several common problems which occur with serial communications, and information on how you could use DLM to diagnose them: 4.1 Hardware Connections You can easily check out the hardware signals by using the "RS-232 Signal monitor". Connecting the DTE to the monitor cable should "raise" the DTR and RTS signals. If this is not the case, either your connections are incorrect, or the DTE device is not online properly. (In some rare cases this may be a normal state for the device). Connecting the DCE to the monitor cable should "raise" the DSR and CTS signals. If this is not the case, either your connections are incorrect, or the DTE device is not online properly. (RI and DCD are not always ON, so you can't expect them to be in a particular state). Once you get the above signals correctly connected, switch to "Begin data capture". Data transmitted from the DTE should appear ABOVE the dashed sepatating line, data transmitted from the DCE should appear BELOW the line. Data Line Monitor Page: 9 4.2 Speed and Data format If the speed of the two sending and receiving devices is not the same, no communication will occur. Assuming you know what the speed SHOULD be, it is easy to recognize data at an incorrect speed with DLM. Capture a good sample of ASCII data with DLM set to the speed and format which you think the communication should be occuring at, and then look at it in review mode. If the data completely readable, the speed and format is correct. If the data is partly legible, but about half of the characters seem to be corrupted, the speed is correct, but you have incorrect PARITY. If the data is completely un-readable, examine the HEX values of several characters (by moving the cursor and looking at the status line). If the data has the high bit set (80-FF), check to see if it would be readable without the high bit set. If this is the case, the speed is correct, but the data format (Data bits/Parity) is incorrect. DATA BITS is the most likely suspect. If the above test does not reveal any readable data, the speed is probably incorrect. This will also manifest itself with "lots" of 'F'raming and 'O'verrun errors. 4.3 Flow Control Many modern devices are not capable of receiving data continuously at the highest speeds supported on the interface. An example of this is a printer which prints 200 Characters per second (CPS), and has a serial interface running at 9600 bits per second which is about 960 CPS. Such devices usually have an internal buffer, which absorbs data at full speed, and stores it so that it can be printed at a slower speed. When this buffer approaches being full, the printer will assert FLOW CONTROL on the sending device, which causes it to stop sending data until it is later instructed to proceed. If flow control is not working properly, the usual symptom is that the first few lines of data are correctly received by the device, after which symptoms vary from "lost data" to "lock up". There are two common forms of flow control, one uses hardware signals, and is called HARDWARE FLOW CONTROL. The other uses reserved data characters, and is called SOFTWARE FLOW CONTROL. Data Line Monitor Page: 10 4.3.1 Hardware Flow Control With HARDWARE flow control, the receiving device will de-assert one of its hardware output leads (DTE=DTR/RTS, DCE=DSR/CTS) to inform the sender to stop sending. When it is ready to receive more data, it will re-assert the signal, and transmission will proceed. Using DLM, you can monitor the hardware signals during data transmission, and see if one of them is lowered to perform flow control. You can also see if the sending devices responds to the flow control (stops sending), and how quickly it responds (by noting how many characters are sent after the signal drops). If the signal dropping appears to have no effect on the data stream, then you know that hardware flow control is not being recognized or acted upon. 4.3.2 Software Flow Control With SOFTWARE flow control, the receiving device transmits a character to the sending device to command it to stop sending. This character is usually CONTROL-S ($13). When it is ready to receive more data, a different character is transmitted. This character is usually CONTROL-Q ($11). Using DLM, you can monitor the data to and from the receiving device, and check for flow control characters. You can also see if the sending device responds to the flow control (stops sending), and how quickly is responds (by noting how may characters are send after the CONTROL-S is received). If a CONTROL-S is transmitted, and it appears to have no effect on the data stream, then you know that software flow control is not being recognized or acted upon. Data Line Monitor Page: 11 5. ASCII code chart Most Significant Figure HEX|| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ===++=====+=====+=====+=====+=====+=====+=====+=====+ 0 || NUL | DLE | | 0 | @ | P | ` | p | ---++-----+-----+-----+-----+-----+-----+-----+-----+ 1 || SOH | DC1 | ! | 1 | A | Q | a | q | L ---++-----+-----+-----+-----+-----+-----+-----+-----+ e 2 || STX | DC2 | " | 2 | B | R | b | r | a ---++-----+-----+-----+-----+-----+-----+-----+-----+ s 3 || ETX | DC3 | # | 3 | C | S | c | s | t ---++-----+-----+-----+-----+-----+-----+-----+-----+ 4 || EOT | DC4 | $ | 4 | D | T | d | t | S ---++-----+-----+-----+-----+-----+-----+-----+-----+ i 5 || ENQ | NAK | % | 5 | E | U | e | u | g ---++-----+-----+-----+-----+-----+-----+-----+-----+ n 6 || ACK | SYN | & | 6 | F | V | f | v | i ---++-----+-----+-----+-----+-----+-----+-----+-----+ f 7 || BEL | ETB | ' | 7 | G | W | g | w | i ---++-----+-----+-----+-----+-----+-----+-----+-----+ c 8 || BS | CAN | ( | 8 | H | X | h | x | a ---++-----+-----+-----+-----+-----+-----+-----+-----+ n 9 || HT | EM | ) | 9 | I | Y | i | y | t ---++-----+-----+-----+-----+-----+-----+-----+-----+ A || LF | SUB | * | : | J | Z | j | z | F ---++-----+-----+-----+-----+-----+-----+-----+-----+ i B || VT | ESC | + | ; | K | [ | k | { | g ---++-----+-----+-----+-----+-----+-----+-----+-----+ u C || FF | FS | , | < | L | \ | l | | | r ---++-----+-----+-----+-----+-----+-----+-----+-----+ e D || CR | GS | - | = | M | ] | m | } | ---++-----+-----+-----+-----+-----+-----+-----+-----+ E || SO | RS | . | > | N | ^ | n | ~ | ---++-----+-----+-----+-----+-----+-----+-----+-----+ F || SI | US | / | ? | O | _ | o | DEL | ---++-----+-----+-----+-----+-----+-----+-----+-----+ Data Line Monitor TABLE OF CONTENTS Page 1. INTRODUCTION 1 1.1 What is DLM? 2 1.2 Hardware Required 2 2. HARDWARE SETUP 3 2.1 IBM P.C. serial ports 3 2.2 Passive Monitor Cable 4 3. USING DLM 5 3.1 Begin data capture 5 3.2 Review captured data 6 3.3 Clear capture buffer 6 3.4 RS-232 Signal monitor 7 3.5 Serial port parameters 7 3.6 Disk transfer functions 7 3.7 Exit to DOS 8 4. DEBUGGING TIPS 8 4.1 Hardware Connections 8 4.2 Speed and Data format 9 4.3 Flow Control 9 5. ASCII code chart 11