reZet80 status

I was away for more than two years due to some real life projects.
But now I'm back with so many Z80 projects and always so little time...

I started work on my first 80s project, the reZet80 SENTINEL with 128 KiB of RAM and LCD display in CMOS technology but I need to distinguish between my CMOS and NMOS Z80s first.
The first reZet80 SENTINEL release will be a game only release including:

• Asteroid Belt

• Hex Invaders

• two-player Black Jack

• Haunted House text adventure

• Hex Man (Hexadecimal Hangman)

In the second release I'll add a NAND memory cartridge and more games:

• Dino Chase

• Camel Race

• Donkey Race

• Obstacle Runner

• The Lighthouse text adventure

reZet80 stands for "Reset me back to the 80s with the Z80".
reZet80 features a set of retro projects to develop computing and arcade systems that resemble the Z80 machines of the late 70s and 80s.
All systems are built from scratch and not copies of any other Z80 system.
The development process includes hardware design and software programming in Assembler.
I started reZet80 back in 2016.

reZet80 releases (including documentation, schematics and source code at GitHub):

• 2023-10: reZet80 PIONEER R1 (Haunted House-only release)

• 2022-12: reZet80 SCOUT R0 (prototype, unfinished code)

• 2022-06: reZet80 PIONEER R0

• 2021-06: reZet80 HWDK R0

• 2021-02: reZet80 DEV R1 (unfinished code)

• 2020-11: reZet80 DEV R0

Off-topic note: The letter Z stands for the company Zilog and the Z80 CPU. The Z is in NO WAY related to the Russian war against Ukraine!

Z80 NMOS/CMOS Test

Since 2016 when I started reZet80 I have accumulated about forty Z80 CPUs.
Most of them are standard Z80s in a DIP-40 package from ebay or unsoldered from old computers.
I also collected some exotic ones like the T6C79 from Toshiba and the ATJ3310 and ATJ3315 from Actions.
But I'll stick to the pure Z80 as produced by Zilog here.

A short history of Z80 CPUs:

• Z80: 2.5 MHz NMOS

• Z80A: 4 MHz NMOS

• Z80B: 6 MHz NMOS

• Z80H: 8 MHz NMOS

• Z80: 4-20 MHz CMOS

I'll talk about the CPU speed in one of my next posts.

A simple 8-byte program will help me differentiate between NMOS and CMOS Z80 CPUs:
;=============================================================================
; take it easy
nop
; disable interrupts
di
; SENTINEL configuration register
ld c, 00h
; out (c), 0
db EDh, 71h
; loop forever
_loop:
jr _loop
;=============================================================================
NMOS CPUs output 00 (hex) executing the undocumented instruction "out (c), 0".
CMOS CPUs output FF (hex).
The SENTINEL configuration register is a 74HC273 latch.
I simply connect eight LEDs to the latch output to display the results:

Zilog Z80A (7725 date) ceramic package, clearly NMOS

Mostek MK3880 (7807 date) ceramic package, NMOS

Mostek MK3880 (8029 date) ceramic package, NMOS

SGS Z8400AD1 (18214 marking) ceramic package, NMOS

Toshiba TMPZ84C00P (8532 date) CMOS, extracted from a YAMAHA FB-01 mainboard.
I bought the FM sound generator from ebay so I can't comment on its history but I expected the CPU to be a genuine Toshiba CMOS part.

SGS Z8400B1 (88207 marking) NMOS as expected

Zilog Z84C0020PEC (0047 date) Bought from a leading ebay seller in China many years ago.
At least it seems to be a CMOS CPU, not a counterfeit NMOS one as expected.

Zilog Z84C0020PEC (0723 date) Also from China, again a surprise, all twelve are CMOS CPUs.

Sharp LH0080A (0940 date) Bought from a German ebay seller, NMOS as expected.

Zilog Z84C0020PEC (1035 date) According to some sources on the internet these CPUs are fake.
Well, at least they are CMOS. Will test speed next.

MME VB880D (X6 marking) NMOS as expected

Sharp LH0080A (546DA marking) Extracted from a YAMAHA CX5M mainboard, NMOS as expected.