512K flash memory internal upgrade - no traces cut

Discussion forums for users of the Cambridge Z88 Portable Computer
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Paul
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Re: 512K flash memory internal upgrade - no traces cut

Post 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.
In theory, there is no difference between theory and practice. But, in practice, there is.
tbug
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Joined: Wed Sep 15, 2021 2:42 am

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

Post 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.
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Paul
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Location: Germanys west end

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

Post 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?
In theory, there is no difference between theory and practice. But, in practice, there is.
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Paul
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Re: 512K flash memory internal upgrade - no traces cut

Post 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.
In theory, there is no difference between theory and practice. But, in practice, there is.
tbug
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Joined: Wed Sep 15, 2021 2:42 am

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

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

Post 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 4.7.1without incident.
tbug
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Joined: Wed Sep 15, 2021 2:42 am

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

Post 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!
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