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+--- Thread: Using 27C128 ROMs in a PC85A board (/thread-377.html)
Using 27C128 ROMs in a PC85A board - CheshireNoir - 25-09-2021
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
RE: Using 27C128 ROMs in a PC85A board - ChickenMan - 25-09-2021
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/showthread.php?tid=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.
RE: Using 27C128 ROMs in a PC85A board - ChickenMan - 25-09-2021
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.
RE: Using 27C128 ROMs in a PC85A board - someone - 25-09-2021
[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)
RE: Using 27C128 ROMs in a PC85A board - CheshireNoir - 25-09-2021
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.