Printer Help

General discussions related to the Altair 8800 Clone

Printer Help

Postby jrdurgan » July 25th, 2018, 8:42 am

Hello All,

I am a very recent user of the Altair clone. I have an Okidata serial printer that I want to use on port 2. I can save myself a lot of experimenting if one of you could tell me what pin on the altair connects to what pin on the Printer. I saw on this forum where one of you had used an okidataa printer, but when I went searching for him I couldn't find the forum entry. I would appreciate a direct contact with the correct wiring. I have really enjoyed all the interesting discussion on this forum. In addition to the Altair, I have an IBM 7155 Portable pc that I bought new in 1984. I used it in Graduate School. It still works and I do a lot of word processing on it still.

Anyway I have a very steep learning curve on the Altair. I have printed out all the pdf manual files, and am now plowing through those. I look forward to hearing from one of you with a suitable wiring for my printer.

Thanks in advance for your support

John D
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Re: Printer Help

Postby TomXP411 » July 26th, 2018, 12:52 pm

Pins 2 and 3 are transmit and receive. Which pin is which depends on whether your device is a DTE (terminal) or DCE (modem, mainframe, host computer, etc.)

The Altair is a DCE device (it's wired like a modem), so you can use a straight-through cable from a PC or dumb terminal.

I believe printers are DTE (terminal) devices. So first, try a straight through DB25 cable. If that doesn't work, use a null modem cable or null modem adapter. Another way to think of it: If a cable lets you print from PC, it's the wrong one. :)
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Re: Printer Help

Postby AltairClone » July 26th, 2018, 4:54 pm

Based on past experience with newer serial printers, they have a very large print buffer. If you are printing shorter documents, the print buffer never fills up and so the handshaking doesn't really matter. In this case, a straight through DB-25 will most likely work since the Altair is DCE and the printer is DTE.

If you want to printer longer documents (e.g., a banner), or if the printer doesn't have a large buffer, then making a cable with the proper handshake wiring is required. There is no need to guess or experiment. Give us the model # of the particular printer you want to connect and we can look up the printer's serial port pinout and which pin options the printer has for handshaking. Then the cable wiring will be right the first time.

Mike
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Re: Printer Help

Postby jrdurgan » July 30th, 2018, 5:14 pm

Hello All,

I appreciate the responses. I will be using a vintage Okidata microline turbo printer. I doubt I will print really long documents, but It would be nice to be prepared.

John D
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Re: Printer Help

Postby jrdurgan » July 31st, 2018, 2:54 pm

Hello All,

I found the following pin wiring diagram on hte internet in an okidata 184 manual. Here it is:

computer printer
PG 1----------------1 PG
TD 2----------------3 RD
RD 3----------------2 TD
CTS 5--------------11 SSD
DSR 6--------------20 DTR AND 6 DSR
SG 7-----------------7 SG
4RTS COUPLED WITH 5CTS

Does this look Reasonable? I have a small connector that can be hard wired in any configuration. I would appreciate any comments you may have on this configuration

Thanks in Advance

J Durgan
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Re: Printer Help

Postby AltairClone » July 31st, 2018, 10:01 pm

Again, what is the specific printer model you have? Then we can determine exactly how to connect the Altair to the printer.

If it is the model 184 in the manual you mention, then it appears you can use a straight through cable as long as you set the serial interface switches in the printer appropriately.

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Re: Printer Help

Postby TomXP411 » August 1st, 2018, 1:27 am

jrdurgan wrote:Hello All,

I found the following pin wiring diagram on hte internet in an okidata 184 manual. Here it is:

computer printer
PG 1----------------1 PG
TD 2----------------3 RD
RD 3----------------2 TD
CTS 5--------------11 SSD
DSR 6--------------20 DTR AND 6 DSR
SG 7-----------------7 SG
4RTS COUPLED WITH 5CTS

Does this look Reasonable? I have a small connector that can be hard wired in any configuration. I would appreciate any comments you may have on this configuration

Thanks in Advance

J Durgan


That's likely for wiring to a PC; as I said earlier, a PC to printer connection is not what you want. I believe you just need a straight through cable.
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Re: Printer Help

Postby jrdurgan » August 1st, 2018, 7:25 am

The printer is an Okidata Microline 184 Turbo. The Serial dips have all been set to the default position

J Durgan
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Re: Printer Help

Postby AltairClone » August 1st, 2018, 11:25 am

1) Use a straight through DB-25 to DB-25 cable with at least pins 2, 3, 4, and 7 connected. It's ok if all 25 pins are connected straight through.

2) Set all serial switches to factory default with the following exceptions:

Bank 1
S7-S8 set to ON,OFF to put the printer's handshake signal on RTS pin 4

Bank 2
S4 set to OFF to disable the check for DSR

3) In the Clone configuration monitor, set the "Port Type" for serial port 2 to 88-2SIO and set "CTS, RTS Usage" to "CTS, RTS Both Used." In the "Admin" menu of the configuration monitor, choose the "Line Printer Controller" option and verify that the "88-LPC (Okidata)" option is selected.

This configuration lets the printer throttle output from the Altair to the printer by de-asserting RTS to the Altair when the printer cannot accept characters (RTS on the DB-25 becomes CTS into the ACIA in the Altair). If the buffer in your printer is large, the printer may never actually have to handshake for a typical small print job.

CP/M uses the 88-LPC printer interface by default. When booting and Altair BASIC disk and prompted for printer type, choose "O" for "O"kidata. The Clone provides the 88-LPC interface by piggy-backing onto serial port 2. We configured port 2 to be an 88-2SIO port because the 2SIO supports a handshake line and the 88-SIO does not (the piggy-backed printer interface inherits the capability of the underlying serial port).

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Re: Printer Help

Postby jrdurgan » August 1st, 2018, 1:25 pm

Mike, thanks so much for this info. I would have never figured all that out.

John D
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