Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs.

Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - Printable Version

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Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - ChickenMan - 27-08-2021

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 -

Filename: pc85_menu.jpg Size: 175.1 KB 28-08-2021, 05:07 PM

Fitted the new roms and powered it up I was now presented with its new Menu -

Filename: pc85b_menu.jpg Size: 192.92 KB 28-08-2021, 05:07 PM

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.

Filename: pc85b_self-test.jpg Size: 126.74 KB 27-08-2021, 05:30 PM

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 Smile

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 Smile

RE: Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - Ernest - 27-08-2021

Good see that you are getting closer to making full use of the PC85's capacity.

If you hit RETURN from the main menu you will get a list of all the available ROM's and can directly launch them from there using standard cursor control to highlight and RETURN to launch.

Just would like to solve the mystery on how to change the labels on those ones that come up as USER ROM?

Ernest

RE: Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - ChickenMan - 27-08-2021

Problem I have is only about a 1/3rd of keys work with even the Return key giving major problems, thats next to fit a new Keyboard kit.

Oh, forgot, its also suggested in the Engineering Notes to fit a heat sink under the 7805 voltage regulator. Because I have some here, one was fitted and it just gets warm after 30min of playing.

RE: Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - ChickenMan - 27-08-2021

I just had a play with ubee512 and replaced the PC85B_PAK4.ROM with a 16k rom with RobotMan in the first 8k and Space Invaders in the second 8k. Running it shows Viatel still on the Main Menu, but if you press RETURN, PAK 4 now shown as User Rom (being RobotMan as an un-known rom) and PAK12 as SpaceInv.

Filename: pc85_roms.png Size: 1.91 KB 27-08-2021, 09:34 PM

Looking at the standard_pc85b_i.rom with a Hex Editor, it seams if your additional Roms are either Edasm, Pascal, Forth, Logo, Type Tut, SpaceInv, Reels, Chess or Survivor they will show up. We have all those as original ROMs except for Reels. I assume it checks the CRC of the roms to determine what they are.

RE: Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - Ernest - 28-08-2021

I suspect more like a signature byte, I think the boot-up to the SHELL menu is too quick to do a CRC check on each ROM every time it boots up.

PS. Even though Self Test doesn't show PAKs 6, 7, 14 & 15 PC85 still checks for and will display in the full menu list, even PAK's 6, 7, 14 & 15.

The only one it will not display is Pak 10 which is reserved for the Menu expansion of SHELL.

Ernest

RE: Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - someone - 28-08-2021

FYI Chickenman, the first 2 photos from your first post are not viewable by someone.

RE: Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - ChickenMan - 28-08-2021

So is the 3rd one visible and its just the first 2 are not? First 2 are JPG files and 3rd one a PNG. All visible to me. Can you try logging out and then see if things change.

RE: Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - CheshireNoir - 28-08-2021

(28-08-2021, 10:00 AM)ChickenMan Wrote: So is the 3rd one visible and its just the first 2 are not? First 2 are JPG files and 3rd one a PNG. All visible to me. Can you try logging out and then see if things change.

I just logged in and 1 and 2 are not visible and 3 is visible.

EDIT: clicking on the images I get the "You do not have permission to access this page." warning.

Chesh

RE: Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - ChickenMan - 28-08-2021

Thanks someone & Chesh, I eventually found the problem, the pictures were actually to small in size, doubled there size and they appear Smile

Hope you guys can now see them.

RE: Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs. - CheshireNoir - 28-08-2021

So other than swapping some ROMs, what other changes are required? I've been looking through the Repository but was unable to find the right Engineering Notes article.

Cheers!

Chesh