80-Bus News


September–October 1984, Volume 3, Issue 5

Page 9 of 47


By Richard Beal

This article gives you all the information and software which you need to set up a print buffer for a serial printer, using a Gemini GM813 CPU+RAM card with no other cards on its 80-BUS, or alternatively a Gemini GM811 CPU plus GM802 64K RAM combination. The print output, in a form suitable for a Centronics printer, is sent from the PIO of the host computer via the GIPB to the serial printer.

A large print buffer allows you to keep using your computer even when you have generated a very long printed report such as a program listing, without having to wait for the printer. This Giant Intelligent Print Buffer (GIPB) operates almost as fast as you can send data to it. For example when listing data to the screen using an SVC, which is very fast, there is no noticeable slowing up when sending the data to the GIPB at the same time.

You may like to develop the idea further, so here are some suggestions:–

– write a version which runs under a normal RP/M or CP/M;
– allow the display of characters in the buffer;
– allow buffering of the characters to an attached disk;
– develop a full automatic print spooling system;
– write a version with serial input and Centronics output.

The User Manual for the GIPB – Version 2.5

This program, called GIPB, is a special version of RP/M designed to perform the specific function of acting as a giant intelligent print buffer. Hardware requirements are:–

  1. a GM813 CPU+RAM card or a GM811 CPU card with extra 64K RAM card.
  2. a serial printer for output.
  3. a cable connecting the PIO socket to the PIO socket of another computer which is set up to output data to a Centronics printer. If the other computer if a GM811 or GM813, or a Nascom I/O card, a 26 way ribbon cable with a connector at each end is all that is needed.
  4. an optional serial keyboard on the printer, or a keyboard on the GM811.

No disk card or video card is required. Since there will normally be no video card the printer also acts as the console output device. See the RP/M documentation for details of operation without a video card. On the GM813 it is simply a matter of linking pin 1 to pin 14 on the link block labelled IC35. On the GM811 connect pin 6 to pin 7 on LKB1.

The card(s) may easily be added to an existing 80-BUS system by plugging it (them) in to the last connector(s) on the BUS. Since this would interfere with the BUS signals, cut all the lines on the motherboard except the power lines, which are 1 to 4 and 67 to 78.

As with RP/M, the UART speed for the printer may be changed by altering location F009 in the EPROM to hold the 2 byte UART divisor. This is normally 417 decimal, stored as 01 Al, giving 300 bps. Printer handshaking is supported in the normal way, if required. This is via pin 8 of the serial connector, which must be high to operate. Connect it to pin 2 if you have no handshake line.

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