80-Bus News


March–April 1984, Volume 3, Issue 2

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1.1Various small items were changed. (The unlikely sequence ESC ESC % % used to crash the system). ‘Delete line and scroll up’ now cleared the bottom line of the display if the cursor was there. (Previously nothing happened.) Cursor addressing, Set, Reset, and Test now accepted nested escape sequences during the coordinate string.
1.2A few small internal changes made. The input buffer (used to hold incoming characters while the screen is being scrolled) was reduced to 64 bytes from 128 bytes, (128 bytes was a bit of a waste), and the internal stack area was increased.
2.0Support for the Rotec keyboard and programmable function keys added, hence the jump to 2.0. The monitor size now exceeded 2k and required a 2732 rather than the 2716 of the earlier releases.
2.1The current release of IVC-MON. Sections of the monitor code were restructured to give a faster response to keyboard poll requests. This has a noticable effect on the screen update rate for operating systems such as CP/M where the BDOS polls the keyboard everytime it outputs a character. Another Escape sequence was added to allow lines to be ‘locked’ at the bottom of the screen.
(3.0?)Although the IVC has now been discontinued one further update of the software is envisaged. (When time permits – don’t expect it tomorow!) This will include SOME of the features that have appeared in the SVC monitor (see below).


With a new design on the drawing board Gemini was faced with the usual decision – Do they use a ‘state-of-the-art’ device and design a system around that and accept the attendant constraints? (e.g. the in-built character set and screen formats offered by some graphics controllers.) Or should they remain as far as possible compatible with the IVC? They – wisely in my view – opted for the latter case.

So following the IVC came the SVC. Why SVC? well they had to call it something and it does bear some relationship to the IVC. In fact it is upwards compatible with the IVC. (i.e. You can replace an IVC by an SVC and 99.9% of programs will continue to run as before.) So what do you get by moving from an “I” to an “S”? Well the Z80A changes to a Z80B (6MHz operation), the screen memory goes up in size from 2k to 8k (although some of it doubles as the character generator), a 256x256 pixel graphics mode appears, a 40 x 25 display option is provided (the 0.01% incompatibility), a UART can be added on a piggy-back board to make the SVC a stand-alone terminal, a range of attributes appears, a buzzer is added, a Gemini serial keyboard can be used and finally you get ESP.

I think that is about enough for now, and so I’m afraid you will have to wait until the next issue for part II to find out about the ESP.


  1. PARKINSON D.W., “Remote Terminals and the Galaxy”, 80-BUS NEWS 1-4 Nov-Dec 1982, pp45-46.

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