Sinclair ZX80 / ZX81 / Z88 Forums

Hi. Yeah, I've been looking (glazed over a bit) at bodo's sourcecode. I'm currently trying to get to grips with a bit of VHDL after installing the ridiculously huge Xilinx ISE Webtool suite. I'll probably go for a 3.3V (5V I/O tolerant) CPLD, as they are so much cheaper than the 5V versions, so I ca...

Looking around my room ( http://home.micros.users.btopenworld.com/my_machines/machines.html ) virtually all have dedicated graphics processors or timing chains using TTL to do the display. So, many will display garbage on the screen if the CPU, RAM or ROM is faulty. Some, such as the BBC Micro, use ...

I thought I would be able to go to bed early now I've completed the ZX80 stuff - I think I have now found something else to keep me going into the early hours

Both Andy's and RetroTechies achievements are inspiring

Thanks !

Grant

Hi RetroTechie.
Thanks for that detailed post - that's great info for me to get on with.

Grant

Brill :) I've never tried any CPLD stuff - I've programmed GALs and microcontrollers (AVR,PIC etc.). I have a programmer (Presto) that can do JTAG, so I think it can do the CPLDs, so the more I see on this forum, the more tempted I am :) If any of you have any pointers on getting started with the de...

1024MAK just beat me to it ;) I would guess the likely cause is the chip sockets. Unplugging the chips and plugging them back in is normally enough to clean the contacts. Edge connectors are always a pain when it comes to dirt/tarnishing. The number of times I have to push and pull a NES, Super Nint...

Hi Rich. The plug that I made from old chip pins ensures the molex connectors are not pushed open any further than if they had the membrane inserted, so they are still usable if a new membrane is needed at a later date. By attaching a connector at the top of the case, the remaining membrane remains ...

I repaired one of my ZX81's several years ago, and it is still working perfectly, despite having been taken apart many times. The keyboard had stopped working due to a cracked connector cable. Here is how I repaired it... http://zx80.netai.net/zx81/ZX81KBRepair.htm ...not under my usual Web domain, ...

I've just checked an issue 3 ZX81 ULA and the scope pictures are the same as the issue 1 ZX81 ULA. Pokemon, please check if you are checking the correct pin. RAM CS is definitely, 100%, as shown above for both issue 1 and issue 3 boards. The double-NOP, RAM CS and ROM CS are identical between issue ...

Hi. These are ZX81 traces from an issue 1 PCB. The DFILE is fully expanded (a screen full of characters on a 1K machine), and I am running FAST mode (don't need to now that I am using an LM1881 circuit to block non-display areas). The lines above and below the active display area are blocked from di...