Using 27C128 ROMs in a PC85A board

CheshireNoir · 25-09-2021, 12:38 AM

Hey all,
I have a question. I know theoretically I can use 27C128 ROMs in a 8328-4 board, but without upgrading the ROMs from A to B ROMs, what can I actually do with them? I stuck a doubled ROM with Kilopede loaded in the bottom 8k and Space Invaders loaded in the upper 8k into the IC24 socket.
If I call PAK2 I get Kilopede. If I call PAK10 (Which I thought called the upper 8k) I get "Option not fitted error".
Am I trying to call the second ROM incorrectly, is there a prerequisite I have missed, or have I burned the ROM incorrectly?

In whatever case, what can I do to access that second 8K or am I barking up the wrong tree here, and what I am attempting is impossible?

As I have a surplus of 27C128 ROMs, if I can get the procedure working, I'd like to fill IC22 and IC23 with double ROM images as well.

Cheers!

Chesh

***ChickenMan*** · 25-09-2021, 02:26 AM

I think your PC85 need to be running the latest PC85b roms. I've updated my PC85 to a PC85b and the 27128 roms work in it fine. I did all my tries first in the ubee512 emulator and if I switched it back to a PC85 the upper part of the roms appear not to be accessible. I never tried it in my real bee though.

Further info at https://microbeetechnology.com.au/forum/...366&page=2

I'll have a look at a Kilopede / Space Invaders combo tomorrow, will try it in ubee512 for both a PC85 and PC85b and report back.

***ChickenMan*** · 25-09-2021, 11:14 AM

I made a Kilopede/Space Invaders 16k rom and using ubee512 as I mentioned above, both programs work fine in a PC85b but Space Invaders (in upper 1/2 of the 27128) was not seen in a PC85.

someone · (This post was last modified: 30-09-2021, 11:43 PM by someone.)

[Updated with corrections]
Someone is guessing that the PC85 & PC85B Menu expects PAKROMS to have specific checksums.
For a PAKROM to be recognised by these menu systems 2 criteria must be met:
A: This checksum is calculated by the sum of the first 256 16 bit words in a PAKROM.
B: The first byte of the PAKROM is 0xC3 for a jump instruction.

If the checksum is not recognised it should appear as a USER ROM.

Some examples.
Space Invaders ROM checksum 0xA8B1 (& first byte 0xC3).
Viatel ROM checksum 0x092E (& first byte 0xC3)

CheshireNoir · (This post was last modified: 26-09-2021, 01:14 AM by CheshireNoir.)

Cheers! I'll stick the upgraded ROMs in and see how I go. Time to break out the TL866 II+.
(I was actually inspired to investigate further by that very post, Somebody)

Chesh

EDIT: Eek! it was ChickenMan who posted the link. My mistake.