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Re: 512K flash memory internal upgrade - no traces cut

Posted: Wed Sep 15, 2021 5:51 pm
by Paul
Correct. That is with all RAM Types with a single BUS.
This does not apply to ROMs because the ROM is normally written by a different computer so datalines and Adresslines need to be in the correct order.

Re: 512K flash memory internal upgrade - no traces cut

Posted: Wed Sep 15, 2021 5:58 pm
by tbug
So how does that apply to this mod? Evidently the OZ upgrade from 4.7 to 5.0 worked for patters yet his ROM A17 is attached to motherboard A18.

Re: 512K flash memory internal upgrade - no traces cut

Posted: Wed Sep 15, 2021 6:19 pm
by Paul
I don't know about the contents of the ROM(s) in the Z88.
A17 and A18 are very high for 8 Bit computers who normally only have A0 to A15 giving 64K.
So with A16 being correct, this is 128K of continuous ROM. What size are Z88 ROMs normally?

Re: 512K flash memory internal upgrade - no traces cut

Posted: Wed Sep 15, 2021 6:21 pm
by Paul
And again, what machine wrote the contents of the flash?
If it's the Z88 itself then it just doesn't bother like with RAM.

Re: 512K flash memory internal upgrade - no traces cut

Posted: Wed Sep 15, 2021 6:31 pm
by tbug
The OZ ROM is 512KB for internal ROM upgrade (to fill the full size of the 512K ROM chip). Only 256KB of that is the OS though, the other 256KB is a file store. Patters states his ROM was flashed by someone else, presumably using a PC Flash programmer but the subsequent upgrade was done by the Z88.

I'm guessing that another issue with having the A17 and A18 address lines swapped (because they are tied to the external ROM slot #2) is that any external cards programmed by the swapped Z88 might not be readable by another Z88 that doesn't have the lines swapped?

Re: 512K flash memory internal upgrade - no traces cut

Posted: Wed Sep 15, 2021 7:47 pm
by patters
I have gone over the photos and double checked. You are correct that A17 and A18 are mixed up for the SRAM connection but, as Paul has mentioned, this has no functional impact.

I do however label A17 & A18 consistently with their actual positions on the motherboard near the card connector. Consequently the correct address lines are indeed linked to the flash memory chip at their expected pins. I can confirm that I have successfully flashed OZ 5.0 in place from OZ 4.7.1 without incident.

Re: 512K flash memory internal upgrade - no traces cut

Posted: Thu Sep 16, 2021 1:55 am
by tbug
You're absolutely right of course and I apologise for making you go over your post again. I got confused by your photos when tracing the wire paths - I should have checked more carefully.

Well, I've spent hours today trying to get my Z88 to recognise my internal 512KB FLASH ROM and have contact traced it three times and re-wired the mod twice; now it looks more like your layout (my wires are now shorter which is good) however the Z88 still thinks it has an EPROM inside and not FLASH and so I can't do an in place upgrade.

I guess I'll just have to bite the bullet and buy a new SST brand FLASH ROM. I'll probably buy the same RAM IC that you used as well, then try the mod again when they arrive.

Really appreciate the help everyone!

Re: 512K flash memory internal upgrade - no traces cut

Posted: Tue May 02, 2023 3:50 pm
by Fecn
I've just upgraded my 2nd Z88 using this forum post as a guide. I now have two Z88s with 512KB/512KB onboard memory.

I thought I'd leave a reply on here just so that others know that this post is still the best upgrade documentation to follow, and to say thank you to Jamie for documenting the process.

Re: 512K flash memory internal upgrade - no traces cut

Posted: Tue Jun 06, 2023 12:14 am
by patters
:lol: I'm not Jamie btw.
Glad there are now a good number of Z88s that have been upgraded without resorting to carving up their boards. May there be many more to come.