• Please review our updated Terms and Rules here

Insert interesting title here !

Gary C

Veteran Member
Joined
May 26, 2018
Messages
2,256
Location
Lancashire, UK
Well its nice to get back to some sort of normal. Quick weeks holiday in Cyprus away from the UK weather to lie on the beach in glorious sunshine and eat Greek food after dark by the sea.
Fantastic.
Did have to have a covid test before flying home and if it was positive would have meant a week in a Cypriot government 'hotel' but the PCR tester barely waved the swab at one nose (no mouth) and a negative meant a nice flight home again.

So, the Osborne. Its working :)

In the end it was 8 RAM chips that had failed. I put together a couple of programs in assembler to test the RAM and the screen and once replaced the screen is bright and clear.

The design was a bit of a surprise. All IO memory mapped rather than using the Z80's ports, page swapping using the self same ports, and having a 9 bit video display, using an extra ram chip to provide an extra bit to control the brightness of the characters. I noted that the manual indicated that the default page 2 mapped the ROM into the lower part of memory, page 1 mapped RAM into this area but the manual seemed to show that page 3 would only have the brightness RAM mapped, which would be odd as once you had made the switch, the code doing the switching would be lost with no way to switch back :)
However this isnt the case as it basically maps in bit 9 over bit 8 (DO7) but the rest remains as before.
The screen memory is also a surprise in the way it implements a viewport in hardware using programmable counters that can be modified to move the viewport around a larger virtual screen.

Learnt so much about the Osborne hardware in the last few months I decided I need to get another non working one and lo and behold, one turns up on Ebay, collection only within range (which keeps prices down) and will be picking it up tomorrow. Its also an earlier unit and has the video shunt which my current unit is missing.

So need to get some software and as such, a Gotek is on its way.
 
So this goes with this? https://www.vcfed.org/forum/forum/genres/cp-m-and-mp-m/1215370-osborne/page3
 
Yep, I just blog what I do for fun and to give myself a timeline I can look back on of what I have done and to make it a bit more social.
 
So, typically, the new broken Osborne works :(

All that hard gained knowledge and no where to practice it on.
 
Back
Top