Scor­pio News

of the catalogue its price had fallen by over £100! SYS 19 was reassembled to include the Winchester split into two drives of 10M each and run. As usual nothing happened! A long read through the manual, combined with a study of the circuit for the GM829 finally showed that the SEL line needed to be active for up to 250ms before timing out, and RST needed a 25us pulse. Both these lines were being driven for the duration of one Z80 output cycle only. The first attempt to correct this added a latch which was set and then reset when RDY went active. However the code involved was not compatible with SIMON or any Gemini BIOS so the latch was replaced by a monostable (74LS123), triggered by SEL and reset by RDY. The Winchester then worked, set up in SYS as a Rodime 20M drive, although with BIOS 3.7 the Command Descriptor Block needs to be found and the last of the six bytes set to zero, otherwise an error code is produced.

The system also includes a GM833 512K RAM disk. This has been increased to 2M bytes by adding a link between all pin is and a further multiplexer (74LS157) to drive this line from A19 and A20. The 4164s have been replaced by 41256s.

A 3.5″ disk drive, also from RS, has been added. Again, a quick read through the paperwork suggested no problems,​but on trying to format a disk the drive stepped very erratically. Yet more research found that a 1.2ms delay was needed after a write operation before side change or track access. The drive code was modified to look for any track seek/​step instruction and add this delay first. BIOS 3 already has a suitable delay built in for other reasons.

Following Paul’s comments on WordStar 4 and how much better it was (WS5 is now out for PC’s) than Version 3, I have now upgraded to this for use with the GM880 card. However many problems have come to light. Because CP/M has very limited memory available, compared to MS-DOS the programme is much more limited and during edit time does not know character widths for proportional spacing, This makes is very wasteful of space on the page, as most lines could include more words than they do. It also cannot correctly centre a proportional line, as it only adds spaces at the start of the line as if for monospacing. I have now worked out a long-winded routine to do this, making use of the printer’s own centring ability, dot commands and custom print functions, QWER. The printer in use is a Facit 9401 typewriter with Centronics interface ‘Compatible with Diablo 630’. However, it has several software bugs itself. It should be able to automatically justify between margins, but each line is short by the same number of units as there are spaces in the line (a space is ten units). In addition if set to auto back print it misses the last letter from every word – not much use!

If anyone wants advice and help on any of the mods and problems above, or can give help with WordStar 4 problems, please get in touch with me on Bristol (____) ______.

How about a Bristol area 80-BUS User Group? ●