Sinclair ZX80 / ZX81 / Z88 Forums

Back in the late 1990s this must have been wonderful. And still may be, if you have a STATIC ram board with battery backup. But now there are Zxpand and other speedy or somewhat-speedy storage solutions. The inventiveness of the ZX81 community has produced, and is continuing to produce, a surprisin...

I have two of those C/W with the correspondence between Paul Hunter and the American customer he sold them to for his Gardening business and can confirm that it was indeed useful in that respect as you could store routines/programs for instant boot-up later, but now superseded by the ZXpand. Briefl...

It may be that one of the ROM chip data bus output drivers is weak. With a RAM pack attached, there is more load on the data bus output drivers. Not every board is the same, as although different chips are logically compatible, there may be slight differences in their electrical properties. Mark In...

Ok, so testing the flaky ROM on another TS1000 with a different ULA (no backporch signal), it won't even boot up. Won't get to the cursor and sometimes throws garbage up on the screen. When put on the TS1000 with backporch signal, at least it behaves mostly normal. Again, can checksum it and it will...

So with my new checksum program (maybe more accurately a really primitive hash) the three ROMs now give different value: ROM 1 = 3424166000 ROM 2 = 3424958100 ROM 3 = 3424957100 Btw, I'm running a somewhat dated EigthyOne (i.e. I downloaded the latest a few years back and I don't tend to update -- I...

Hmm, then somehow a reordering of instructions could cause the same checksum. Or, some unlikely occurrence of taking away and adding instruction that results int he same value. I'm going to re-try computing the checksum using this modified code: 10 FAST 20 LET A = 0 30 FOR B = 0 TO 8191 40 LET A = A...

Moggy wrote: ↑Sun Oct 20, 2024 4:50 pm You have a 622 2nd issue ROM, a final issue 649 and the Motorola one I believe is also a 649.

They all have the same checksum...isn't the content in all three the same?

I did clean the pins on the Motorola ROM and no change. It also seems to give the best picture through RF when RAM pack installed. I've noticed over time that if the a RAM wobble occurs, the picture interference gets less. So somehow it seems that ROM is impacted RAM.

Is it just a timing issue then with 16K (i.e. does the RAM pack slow it down enough so it doesn't need the PAUSE?)

I posted in a new topic about why it fails with error code 2 or 4 when using a RAM pack...turns out its a faulty ROM that still checksums properly.

I changed the pics to PNG....