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Chapter C Making An RS232-C Serial Interface Cable
(User's Guide ML192/ML193 (IBM))
RS232-C Serial Interface Cable Information
If you have purchased the optional Super Speed RS232-C serial interface, APPENDIX BDatabase 'Users Manual for ML192/193 IBM ', View 'Table of Contents' contains all the necessary information for installing the board and setting its function switches. This appendix is only essential for those who decide to make their own cable or have one made.

The IBM-Compatible MICROLINE 192 and 193 printers require a four-conductor shielded cable no longer than 50 feet (15 meters). You will need on the printer end:

1. a 25-pin plug, equivalent to a Cannon DB-25P

2. a connector shell, equivalent to a Cannon DB-C2-J9

on the computer end:

1. a 25-pin socket, equivalent to a Cannon DB-25S

2. a connector shell, equivalent to a Cannon DB-C2-J9

Here is the serial cable configuration:

NOTE: You must use a shielded cable, and connect the end of each shield to the frame ground of each unit.

Figure C-1 illustrates the position of the pins on the connector.


If you want to learn more about the R5232-C interface signals, the signal chart below and the pinout chart (see below) describe them in detail.

PGAAThis signal, Protective Ground, on pin #1 (printer's side) is connected to eliminate transmission noise and to prevent electrical shock in case of a short circuit.
TDBAThis signal, pin #2 on the printer's side, is the printer's Transmit Data (TD) line.
RDBBThis signal, pin #3 on the printer's side, is the Receive Data (RD) line. This line must be connected to the computer's Transmit Data (TD) line.
DTRCDThe Data Terminal Ready (DTR) signal is pin #20 on your printer, and is used by most computers to monitor the printer's ready/busy line. When this line is selected, SW1-7 and SW1-8 must be set to ON>
RTSCAThe Request To Send (RTS) signal is pin #4 on the printer's side and is often used with Print Ready/Busy protocol to send the printer's busy signal when a computer does not have a DTR line. When using the RTS line, SW1-07 must be ON and SW1-8 must be OFF. RTS becomes LOW(-) when the printer is busy, and HIGH (+) when the printer is ready to receive.
DSRCCWith the Data Set Ready (DSR) signal (pin #6 on the printer), the computer notifies the printer when it's ready to transmit. When the computer doesn't have a DTR or a CTS signal, this pin is connected to the printer's pin #11.
SSD*_The Supervisory Send Data (SSD) line is pin #11 on the printer. It is the printer busy line for Printer Ready/Busy protocol. This busy signal becomes active when the printer's buffer is full and can no longer receive data from your computer. The IBM computer looks for a LOW on the SSD line, so SW1-7 must be OFF and SW1-8 must be ON>

*OKIDATA printers provide this SSD signal on pin #11 to prevent buffer overrun situations where several characters or lines of data can be lost. You can choose a signal that is BUSY when negative (-) LOW or positive (+) HIGH with the setting of serial board function switches SW1-7 and SW1-8. (See the function switch table in Appendix B).Database 'Users Manual for ML192/193 IBM ', View 'Table of Contents'

Pin #SignalSymbolDirectionDescription
1Protective GroundPG-Connected to printer frame (Frame Ground).
2Transmitted DataTDFrom printerSerial data signal is used to transmit data from the printer.
3Receive DataRDTo printerSerial data signal received by the printer. Necessary in all applications.
4Request To SendRTSFrom printerTransmission request signal from printer. Can be used as the printer's busy output line for systems using Printer Ready/Busy protocol. HIGH (+) during transmission. IF SW1-7 is ON and SW1-8 is OFF, RTS becomes the printer's busy signal (LOW (-) when BUSY).
5 Not used
6Data Set ReadyDSRTo printerActivated by setting SW2-4 ON. Used as an input line only for computers which send a DSR signal.
7Signal GroundSG-Connection required for all systems to eliminate static on the line during transmission.
8-10Not used
12-19Not used
11Supervisory Send DataSSDFrom printerCan be used as the printer's busy output line when a computer uses the printer Ready/Busy protocol. When SW1-7 is OFF and SW1-8 ON, SSD is a printer busy line (LOW (-) when BUSY). When SW1-7 and SW1-8 are OFF, the SSD line is a printer busy signal (HIGH (+) when BUSY). If DTR is used as the busy line, both SW1-7 and SW1-8 must bet set to ON.

Data Terminal ReadyDTR
21-25 Not used

RS232-C Local Test

After you've configured an interface cable for your computer and printer, you may want to spend a few extra minutes designing a test connector. This test connector can be used to monitor the operation of the interface. Simply follow these instructions.

Using a Cannon DB-25P plug, jumper the following pins:

Make sure the printer is off, then set function switch SW1-5 to ON and Switch SW1-6 to OFF. This places the printer in the circuit test mode. Now you can run the RS232-C local test:

1. Plug the test connector into the serial interface receptacle.

2. Turn the printer ON. The serial interface will check the memory function of the printer's message buffer, the RS232-C interface driver, and the receiver circuit, and then print all the characters.

3. This test can be stopped only by turning the printer OFF.

4. The test produces the following:

a. The firmware revision number is printed.

b. LOOP TEST is printed.

c. The message buffer size is printed: RAM2K OK

d. The printer checks the memory function of the message buffer, then prints

IF OK (interface OK) if the memory check is good, or

IF BAD (interface bad) if the memory check is faulty.

NOTE: If BAD is printed, call your dealer for assistance.

Possible reason for IF BAD: Faulty pin connections with the DTR and DSR signals.

e. Hexadecimal characters from 20 to 7F are transmitted through the TD (Transmit Data) line, and received through the RD (Receive Data) line, then written to the message buffer. The above hexadecimal characters are then printed.

f. This pattern repeats until you turn the printer OFF.

After you've completed the interface test, reset SW1-6 to ON for normal printing operation. Make sure the remaining Super Speed RS232-C function switches are set correctly for operation with your computer (see APPENDIX B). Database 'Users Manual for ML192/193 IBM ', View 'Table of Contents'
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