Z80 NMOS 8MHz instead of Z84C0020?

[LuckStilon]

For some time now it has become increasingly difficult to buy the Z84C0020 (CMOS 20MHz) processor. ZiLOG has ended their production, and the Chinese are massively cheating: they are repainting Z80 NMOS 8MHz processors to Z84C0020. Out of 10 bought from them, 7 are cheated, and this proportion increases over time because people returns them fake chips. Is it possible to modify the project for these processors? I mean using NMOS instead of CMOS and limit the maximum speed to 7 MHz.

[UzixLS]

Great work around NMOS Z80 has already been done in commit 8e09254 (see also https://t.me/uzixls/92 and https://t.me/uzixls/93), but further investigation is needed as this commit breaks compatibility with some SRAM chips.

[LuckStilon]

Oh, great news! I see you did a big job! I'm still using the 2022-10-02 version, which is probably why I still had the problem. I have a few dozen NMOS processors. I'll try to test them on the latest version and come back with statistics. Luckily, I use only one version of SRAM, from one reliable source (tme.eu). Here's my test bench :-) Thanks!

[UzixLS]

New version isn't released for now as it requires further improvement.

[LuckStilon]

I have an "alpha" pof and rom files, version dated 2024-01-28 from somewhere. Should be enough for testing.

Additionally - is it possibly to add parameter "CPU type" (NMOS/CMOS) to MAGIC->Advanced menu? Switching to NMOS would limit the processor speed to 7MHz (instead of 14 MHz) during SD card operations in Auto CPU - ON mode, and limit the speed selection to a maximum of 7MHz. If I remember correctly, the fastest NMOS processors were manufactured for 8MHz.

[UzixLS]

I don't like idea to have 9999 configuration options in menu, but it's possible to autodetect NMOS CPU at boot time and automatically limit speed for "auto cpu freq" option.

[UzixLS]

CPU type autodetection was implemented in commit 23445b4 and ll be included in the next release.

[LuckStilon]

Great news! Some time ago I tested over 25 NMOS processors and modified the ROM for my needs: removed the autoturbo parameter and the 14MHz speed.

Are there any things in the current version of the code that are known to work incorrectly and needs to be fixed?

[UzixLS]

There are known issues after commit 8e09254 - it's breaks compatibility with some bootleg SRAM chips, which works almost fine with previous version.