ROMulator Z80 - First Test!

#romulator #z80 #vintagecomputer
First test of a project that I've had in the works for a while now - the ROMulator Z80! Testing out some basic features on a Timex Sinclair 1000 with a Z80 processor.
More information at:

ROMulator 6502:

If you haven't seen them yet, check out Adrian Black's videos using the ROMulator 6502:

[RudysRetroIntel]

Simply amazing! Once I get my ROMulator for 6502, I will be ordering this one. Timex sinclair prompt: K" indicates an expected BASIC keyword (GOTO, GOSUB, etc)

"L" indicates an expected literal (i.e. numeric constant or variable name)

"F" indicates an expected function (SIN, COS, etc)

"G" indicates an expected graphics character

[markevans]

The ZX80 & ZX81 (T/S 1000) use some clever tricks to have the CPU do most of the work in generating the display.
It's easier to see what is going on from the ZX80 schematic. Since the same logic is implemented by standard TTL logic chips.

Both the ROM and RAM appear at multiple addresses.
For the ROM this is 0000-1FFF, 2000-3FFF, 8000-9FFF, A000-BFFF
For the RAM this is 4000-43FF, C000-C3FF (1K) 4000-47FF, C000-C7FF (2K) 4000-7FFF, C000-FFFF (16K)

What's used as the video memory is the copy between C000-FFFF.
The reason for the cursor changing to an inverse G is the system variable MODE. According to the manual, this is at 16390 (4006) though it looks like it's 49158 (C006) which the ROM actually uses.
What should work with the ROMulatior would be to add 14k of RAM between 4800-7FFF mirrored at C800-FFFF. Replacing the internal RAM requires holding RAMCS high on either the ULA or the edge connector.
RAM expansions larger than 16K for the ZX81 would only enable the external RAM between 8000-FFFF for none instruction fetch operations. Emulating these would require M1.

[seanwilliams]

I have a stack of Z80 machines so I'll be ordering a few of these when they're done. Keep up the good work!

[____________________________.x]

Excellent, this is just want I need, well done on developing this, and trying to get it to work on a ZX81 is really impressive 🙂

[retroobsession]

Your 6502 Romulator was a god send for me. My PET suddenly stopped working about 2 days after the Romulator arrived and it has given life to me until I get in a position to burn new ROM chips. I will definitley buy a Z80 version when finished

[XTronical]

Brilliant, look forward to the final version

[pparadigm]

Very nice, looking forward to the release version.

[kjtroj]

Excellent! As a TRS-80 collector, I'm very interested in this!

[TheTrashcutter]

I am a simple man: i see ZX81 in thumbnail, I watch and like

[sorcererstan]

Awesome, looking forward to it. Always been a Z80 guy, ever since my Exidy Sorcerer and Kaypro computers

[ianshippen]

If I remember I think your additional RAM will need to disable the internal 2K as it is possibly clashing as Sinclair cut a lot of corners and the internal RAM could be repeating in 2K blocks all the way up to 32767

[patrickbodine]

My first computer. Created fractal images.
Fun stuff.

[daishi]

When I was 10 I ordered the ZX81 kit and built it om my parents kitchen table.

[cathyfarcks]

Zxiq doesn't have "video memory" as such, the video signal is generated by software. The screen contents are actually stored in a movable "list of terminated strings" structure. I'm not certain after 40 years, but I think the line terminator is a C9 RET opcode for some reason.
Makes sense that what's breaking is either IO addresses being treated as memory addresses by your hardware, or the high bit of the address bus being used by your hardware where the ZX81 itself ignores it - as you thought.

[dannyarnold]

Sign me up, I have been successful using my 6502 romulator to debug my own projects ever since Adrian Digital Basment's episode was out, Its such a invaluable tool I expect this new one will be just as great.

[elektronkim]

"G" is the input mode for one of the graphics characters. It's from a keyboard combination or the forever running machine code went to some wrong place. I'm some kind of ZX-Spectrum teen freak from back then.

[westleygress]

This was my first computer. Was still working all this time until last month.

[TVPiles]

Just a tip here, you were probably interfering with the keyboard mapping. The ram switches oiff on thge Sinclair when the keyboard is read.

[marianaldenhoevel]

Isn't it lovely what new computers can do to old computers?

[MichaelDoornbos]

Pretty great. I really need this for a W65c02S ;)