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#commodore128

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Home Computer

Mi actual mesa de trabajo:

- Panasonic FS-A1 mk2 MSX2 con cartuchos Mapper/Megaram de 512K y ObsoNET

- Sinclair ZX Spectrum 128 +2A (x2) con Dandanator + Multiply

- Texas Instruments TI-99/4A con FlashROM99, expansión de 32K y adaptador para joysticks

- CZ Spectrum y CZ Spectrum plus con Dandanator + Multiply

#commodore64#c64#amiga500
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ytm

In github.com/ytmytm/c128-z80-8mh project issues someone suggested trying Z280 CPU instead.

Today I ran some tests on this daughterboard.

Unfortunately it doesn't work as it should yet - the computer doesn't enter C128 mode.
The test program that I put into diagnostic ROM (offset $5000 within ROM, that appears at $0000 for Z80 after reset).
The program just increases border colour in a loop:

LD BC, $D020
LD A, 0
LOOP: OUT (C), A
INC A
JR LOOP

I get different patterns at normal clock (2 cycles / within low phase of 1 MHz tick), at dot clock speed (4 cycles), at doubled dot clock (8 cycles) and even at quadrupled (16 cycles). With faster clocks I have to reset mutliple times until correct startup. With normal clock it works almost every time.
Once it starts it's completely stable, won't lock up randomly.

I also get different patterns with Z280 memory cache enabled, so I suppose that feature works too:

LD C, $12 ; cache control register
LD L, 00001000b ; enable data cache, enable code cache
.db 0edh,6eh ; ldctl (c),hl

I gather from this that:
- the circuit in general works and I got the shared address/data bus right
- reading code from ROM works
- outputing data to I/O works

A Z80 diagnostic code that doesn't use RAM would be nice. Right now I can't enter C128 mode, so I have no way of testing memory access without writing some more elaborate Z80 code and I'm not Z80 coder.

Project files attached to the issue: github.com/ytmytm/c128-z80-8mh

#c128#commodore128#z80
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