80-Bus News


January–February 1983 · Volume 2 · Issue 1

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serial port. This could make a very economical solution to many engineering problems. It would be interesting to know what applications RP/M is being used for – why not write an article about yours?

Now to bring you up to date on RP/M. The first release was Version 0.1, which was issued with all GM811 boards until recently. This version was quite successful as a first attempt, since it had no reported bugs! However there were a number of areas for improvement to the design, and when the GM813 was produced and the Micropolis eighty track drives appeared, a new version was required. Version 2.0 was issued in June 1982, and like the original still has no reported bugs. The description of Version 2.0 below, which describes the changes made, may convince you to try to persuade a Gemini dealer to sell you one.

The introduction of add-on memory mapped RAM cards introduced a small problem since if you put together a system comprising a Gemini GM811 CPU card, RP/M Version 2.0 and the MAP 256K RAM card then unfortunately it doesn’t work at all. Any other combination is all right, so if the CPU is a GM813, or if the system is a GM811 with RP/M V0.1 (which is more likely anyway), then there is no problem. The reason is to do with the memory addressing ports chosen by MAP, which unfortunately conflict with the way RP/M finds out whether it is plugged into an 811 or an 813.

The good news is that a very simple modification to RP/M cures this problem completely and has no unpleasant side effects. Gemini will (once the old stocks are used up) be issuing RP/M Version 2.1 as standard for 811 and 813, but for those of you with V2.0 and an EPROM programmer able to cope with the 2732, here is a complete description of the changes between 2.0 and 2.1.


The first change simply updates the version number, and the rest reverses two instructions. Please note that some people investigating this problem have suggested other changes. These will cause bad things to happen if the RP/M is used in an 813, and the changes described here are the only official ones. By the way, please do not ask Gemini to replace your V2.0 with V2.1, as they will not be amused! I suspect that since most GM811s have V0.1, less than 10 people in the world will ever put together a system which requires this change, and these people should ask MAP for help. Credit goes to Gemini for issuing V2.1 at all, since MAP are in competition with them. This reflects their awareness of the benefits that result from cooperation over the 80-BUS and keeping the whole array of products from different suppliers compatible.

As promised, here is the description of RP/M V2.0, which all V0.1 owners should study carefully.



The disk boot routine operates with both Pertec DD/DS drives and Micropolis DD/<SS or DS> double tracking drives.

Operates both with original GM811 and new GM813 CPU cards.

Automatic disk boot on power-on or reset if a disk card is in the system.

Operation is possible without a video card, using the serial interface.

Support of parallel printers is included.

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