Sinclair ZX80 / ZX81 / Z88 Forums

Here it is (incl. 50 Hz screen flicker)

You should replace the black stripes by real slots (for better cooling) ..

As I have already written in the other thread: bend the ram's pin /OE up and connect it to the Z80 /RD signal (e. g. at the edge connector).
That solves the timing problem during WRITE cycles ....

Siggi

I've compared the Hitachi chip against the half K chip read cycles and it looks like /OE is doing nothing. Looks like the whole thing is driven by the /CE and I should instead tie /OE to ground? Or do I have that wrong? This diagram shows a "Read Cycle (1) (/CE controlled )" Maybe it has also a dif...

1.) Sinclair invested exactly nothing in decoupling capacatitors, but CMOS rams like them (typically 100 nF tantalum)
2.) There might be a well-known timing problem:
https://www.sinclairzxworld.com/viewtop ... 078#p39078

HTH Siggi

Pin 35 of ULA is the ocillator input:
There should bei pulses @ 6,5 Mhz

Siggi

What is your most favorite instruction/feature when coding on the Z80 in assembly? On the ZX81 that is the feature that code can be executed during line display, the call to upper memory. In hires I use this mainly to prevent display of a user defined character. In lowres it is used by the system w...

dr beep wrote: ↑Tue Nov 07, 2023 8:09 pm Now I use emulation only which is easier since I can do things while on the road with my laptop.

Me too:
ZX81 laptop with Lego docking station:
https://forum.tlienhard.com/phpBB3/down ... hp?id=2612

dr beep wrote: ↑Tue Nov 07, 2023 8:09 pm I played on a ZX81 in the '80s but never had one.

Did you use a Zeddy emulator or a ZX81 of someone else?

Works as expected. :mrgreen: Thanks a lot Siggi PS: Meanwhile I think, that the USB-driver interface (using sysvars SEED and COORDS for return values), which has been designed for usage by BASIC-programs and was later enhanced for usage also by m/c programs, should get a new m/c interface (using reg...