Help with Homemade ZX80-81- HIRES problem

Discussions about Sinclair ZX80 and ZX81 Hardware
User avatar
PokeMon
Posts: 2264
Joined: Sat Sep 17, 2011 6:48 pm

Re: Help with Homemade ZX80-81- HIRES problem

Post by PokeMon »

siggi wrote: Sat Nov 25, 2017 1:51 pm That is wrong! /MREQ IS active during refresh, but it is much shorter active than during nomal READ/WRITE cycles:
Yes - or something like that.
I had that in my mind that it is wrong (and unnecessary) to use /MREQ for character map fetch but was too lazy to research why. :mrgreen:

Anyway the ZX80 video part is different to ZX81 and here the shift register is loaded definitely on the beginning of the (next) /M1 cycle or better rising edge of T1. This has still active refresh signal from previous /M1 but /MREQ is long gone (half clock cycle or 150ns).

Bildschirmfoto 2017-11-25 um 14.42.33.png
Bildschirmfoto 2017-11-25 um 14.42.33.png (30.57 KiB) Viewed 1278 times
Luciano
Posts: 36
Joined: Sat Jan 02, 2016 4:57 am

Re: Help with Homemade ZX80-81- HIRES problem

Post by Luciano »

Yes.. all wires soldered manually.. :D

zx81 KIT.. development board
Post Reply