27-08-2021, 05:40 PM
For another "while in Lock-Down" project, I thought I would look at upgrading my Microbee PC85, first version, to a PC85 II as Microbee called it but generally known as a PC85b. Reading Engineering Notes ECN 24-071185 it quotes -
UPGADING TO PC85 version II
All coreboards, versions 8328-4 and 8328-6, will take 27128
EPROMs in the PAK locations. Some early PC85's had 8328-2
coreboards and these have to be modified to use 27128 EPROMs.
My PC85 has a 8328-4 coreboard, so all is good as no mods needed. We have a complete set of original PC85b ROMs in the repository (Microbee\Software\ROMs\PC85\Standard_pc85b) so I burnt out roms E(2764), F(27128), G(27128) and I(2764). ROM H is normally the Viatel ROM which you can select from the Menu and I already had one of these.
The original PC85 on power up presents you with this Menu -
Fitted the new roms and powered it up I was now presented with its new Menu -
As you can see there are extra options now available because of the extra ROMs fitted. Self Test is no longer on the Menu, but still available via the TEST option in Telcom. The Monitor is also available via Telcom or the usual RESET-M. Running the Self Test, it indicates its checking for all PAK roms installed with none in PAK 9, 12 & 13.
I will never use the Viatel option, so, from the Repository files, I combined the Space Invaders ROM for the first 8k (0 to 1FFFh) and RobotMan for the second 8k (2000 to 3FFFh) into a new image, then burnt it to a 27128 EPROM and finally replaced the Viatel (H) rom with it. Powered up and selected V (Viatel) from the Menu and Space Invaders instantly started and had a good play, as expected. Reset the Microbee and from the Menu selected Basic (B). From Basic I then typed in PAK12 and RobotMan instantly started and also had a good play. Fantastic, so can now burn Rom I normal code into the first 8k of a 27128 eprom and another game in the last 8k which I would access with PAK13 from Basic. Also do the same with Rom E with another game in the 2nd 8k of a 27128 eprom and access with PAK9 from Basic. Unfortunately I ran out of 27128 eproms to do the last 2 eproms, but more are on their way. By replacing the Viatel, I and E roms with 27128 eproms, you now have 4 games (or other programs) available almost instantly without having to load them in by Tape. If I left the PC85 in its original state, its possible to add 8 x 8k games or 2 x 8k and 3 x 16k games. Personally I think 4 is enough
I will then type up a small label of the commands to access the 4 games and glue it to the inside of the top cover (which is never screwed down) for future reference as I'm sure I will forget. Now to get busy playing these games
UPGADING TO PC85 version II
All coreboards, versions 8328-4 and 8328-6, will take 27128
EPROMs in the PAK locations. Some early PC85's had 8328-2
coreboards and these have to be modified to use 27128 EPROMs.
My PC85 has a 8328-4 coreboard, so all is good as no mods needed. We have a complete set of original PC85b ROMs in the repository (Microbee\Software\ROMs\PC85\Standard_pc85b) so I burnt out roms E(2764), F(27128), G(27128) and I(2764). ROM H is normally the Viatel ROM which you can select from the Menu and I already had one of these.
The original PC85 on power up presents you with this Menu -
Fitted the new roms and powered it up I was now presented with its new Menu -
As you can see there are extra options now available because of the extra ROMs fitted. Self Test is no longer on the Menu, but still available via the TEST option in Telcom. The Monitor is also available via Telcom or the usual RESET-M. Running the Self Test, it indicates its checking for all PAK roms installed with none in PAK 9, 12 & 13.
I will never use the Viatel option, so, from the Repository files, I combined the Space Invaders ROM for the first 8k (0 to 1FFFh) and RobotMan for the second 8k (2000 to 3FFFh) into a new image, then burnt it to a 27128 EPROM and finally replaced the Viatel (H) rom with it. Powered up and selected V (Viatel) from the Menu and Space Invaders instantly started and had a good play, as expected. Reset the Microbee and from the Menu selected Basic (B). From Basic I then typed in PAK12 and RobotMan instantly started and also had a good play. Fantastic, so can now burn Rom I normal code into the first 8k of a 27128 eprom and another game in the last 8k which I would access with PAK13 from Basic. Also do the same with Rom E with another game in the 2nd 8k of a 27128 eprom and access with PAK9 from Basic. Unfortunately I ran out of 27128 eproms to do the last 2 eproms, but more are on their way. By replacing the Viatel, I and E roms with 27128 eproms, you now have 4 games (or other programs) available almost instantly without having to load them in by Tape. If I left the PC85 in its original state, its possible to add 8 x 8k games or 2 x 8k and 3 x 16k games. Personally I think 4 is enough
I will then type up a small label of the commands to access the 4 games and glue it to the inside of the top cover (which is never screwed down) for future reference as I'm sure I will forget. Now to get busy playing these games
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ChickenMan
ChickenMan