4mb RAM upgrade - weird GEM text

[coonsgm]

So I upgraded a 520STM with the 4mb @agranlund PCB. The diagnostic cartridge shows everything is looking great, but I get to the desktop and see this:

IMG_1927.jpg (218.69 KiB) Viewed 536 times

Booting games and most other software looks just fine. I've checked a load of different points that could have gone wrong (I do have the bodge wire added to the RAM board), but I'm wondering if anyone else has seen something like this before?

[russellnash]

I saw something like it with the 1mb piggyback upgrade on my 520 ST. When I swapped the CAS1H and CAS1L connections around it was gone.

[coonsgm]

That did the trick. Thank you!

[russellnash]

I am glad that the massive frustration I caused myself by being so stupid as to do a piggyback upgrade was useful to someone.

[Badwolf]

I'm intrigued by this. What's the mechanism at play here? Why does it 'work' until the menus are drawn?

BW

[coonsgm]

It doesn’t just work until the menus are drawn. I was able to run the diagnostic cartridge with a full ram test and pass. Ran through Frontbench as well.

[chronicthehedgehog]

I suppose word read/writes aren't affected. Perhaps the ram test just read/writes words so CSH/L are both asserted, so which way round they are doesn't matter

OR, if you only r/w bytes I suppose it wouldn't matter either

[Badwolf]

I suppose word read/writes aren't affected. Perhaps the ram test just read/writes words so CSH/L are both asserted, so which way round they are doesn't matter

OR, if you only r/w bytes I suppose it wouldn't matter either

Ooooh. So it's high and low bytes (rather than high and low banks, which is where my brain went)?

So word access is fine, byte access would have ...extremely amusing consequences on write!

BW