80-Bus News


January–February 1983, Volume 2, Issue 1

Page 40 of 56

It is even possible to operate the system with no video card and no serial terminal, but with a keyboard on the CPU card (GM811 only) and a parallel printer for output, by turning on the computer and immediately using the S command without being able to see the serial output, to turn on the parallel printer.

There are several limitations on the facilities provided if there is no video card. No screen edit mode or screen dump is available. Also, no cassette input or output will operate, and use of the R or W commands results in an error message.


For certain applications it may be convenient to modify certain default values used by RP/M. These may easily be changed when using RP/M by using the appropriate command, but if access to an EPROM programmer is available then some initial values may be changed. These are stored at fixed locations in RP/M.

F009 contains the two byte value used as the UART divisor. The normal value is 417 decimal, 01A1 hex, which is stored as Al 01. This gives a speed of 300 bps (30 characters per second).

F00B contains the initial value of the IOBYTE. This is 01H, giving a serial printer. Change to 81H for a parallel printer.

F00C contains the number of lines per page. This is set to 66 decimal, 42 hex.


If a form feed character (0CH) is output to the video card by a program, this is translated to a carriage return and line feed.

While the console input routine is waiting for an input the cursor is displayed as a blinking underline. Otherwise the cursor is displayed but does not blink. This overcomes problems relating to programs that scan the console for an input instead of calling the console input routine.

An attempt to boot a disk, whether successful or not, does not change the contents of the program area. This allows a disk to be booted and then a Save command to be issued, providing another means of moving data between an RP/M and a CP/M system.

If an attempt is made to boot a disk without a disk card in the system, then an error message is output. Previously this could cause the system to hang up.

The screen editing logic has been improved to return the correct console status when an edit buffer is pending.


Please notify us of any problems with RP/M, as well as any suggestions for its improvement. We hope that this new and more advanced version will be as free of errors as the original version.


by RICHARD BEAL & D. R. Hunt

The DH bit:

I had almost completed my review of the MAP RAM by the copy date of the last issue, but lack of time did not allow me to finish, so when Richard produced his review of the card with particular emphasis on the software side of matters, I scrapped my review in favour of the following as his is far more thorough. However, Richard has not covered the obvious points concerning the hardware so I will detail them here.

The card is a NASBUS/80BUS 8" x 8" card similar in appearance to all the existing RAM cards, and particularly the Gemini GM802, in that it contains a block of RAM surrounded by the necessary decoding and driving logic. The board is

This is an OCR’d version of the scanned page and likely contains recognition errors.

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