Z280 to Z80 adapter revisit | MSX Resource Center (Pagina 6/9)

Van Edevaldo

Master (154)

05-12-2018, 17:22

I need to apologize to Lintweaker for taking his topic "off-topic".

Van Grauw

Ascended (10707)

05-12-2018, 19:33

I just took it back on-topic to the Z280, don’t worry .

Okay, this is interesting… the R800 MULUB A,r and MULUW instructions have the same opcode as the Z280’s MULTU A,r and MULTUW HL,rr instructions. I’m really gonna have to try some stuff now…

Edit: Okay, so far of all the Z280 opcodes I’ve tried, none seem to have any effect. Would’ve been too good to be true if some of them worked I guess . It’s got some great additions to the instruction set. But anyway, R800 compatible at least (see above), so could be a good replacement. And if configured right, I think it can access the bus with MSX standard timing.

Van PingPong

Prophet (4095)

05-12-2018, 19:51

about FPGA - V99x8 emulation timings details are not so known.
Expecially for V9958 ( V9938 had some detailed timings done some years ago via a digital analizer) there is not much under the day light. For example no one knows about the timings of the WAIT line, nor in what specific situations is activated and what is the delay when this line become active.
Plus it is suspected that the VRAM bus access timings may depend on the values of the horizontal scroll register but no one knows about.....

Van Grauw

Ascended (10707)

05-12-2018, 23:59

https://www.msx.org/wiki/R800_Programming#Changed_instructions

Quote:

Undocumented Z80-operation "SLL" have been replaced with another undocumented instruction similar to "TEST" of the Z280

I tried this, on R800 this opcode (CB 30-37) seems identical to SLA.

(Which actually is a correct implementation for SLL, the Z80 does not do a logical left shift.)

Goes to show there are a lot of myths about the R800 undocumented opcodes that people just repeat to each other without verifying by testing :). Also the Z280 does not have a “TEST” nor a “TST” instruction. On Z280 this opcode is used for “TSET”, but it’s very different from what the R800 exhibits.

Van erpirao

Paragon (1314)

07-12-2018, 15:15

Grauw wrote:

https://www.msx.org/wiki/R800_Programming#Changed_instructions

Quote:

Undocumented Z80-operation "SLL" have been replaced with another undocumented instruction similar to "TEST" of the Z280

I tried this, on R800 this opcode (CB 30-37) seems identical to SLA.

(Which actually is a correct implementation for SLL, the Z80 does not do a logical left shift.)

Goes to show there are a lot of myths about the R800 undocumented opcodes that people just repeat to each other without verifying by testing :). Also the Z280 does not have a “TEST” nor a “TST” instruction. On Z280 this opcode is used for “TSET”, but it’s very different from what the R800 exhibits.

I am reading the thread that you have opened comparing the r800 and z800 / z280, and, without having any idea of programming or hardware, I am looking very interesting.

Van АIеks

Paladin (949)

07-12-2018, 20:04

АIеks wrote:

Everything is real-MSX-EXT. z280 7?

ProtoModule CPU Z280.

Van lintweaker

Champion (457)

07-12-2018, 21:38

АIеks wrote:

Everything is real-MSX-EXT. z280 7?

ProtoModule CPU Z280.

Nice solution for setting the bootup bus timing parameters!

Any reason not to use oscillators for the clocks?

Van АIеks

Paladin (949)

17-12-2018, 15:33

ProtoModule CPU Z280

Van erpirao

Paragon (1314)

17-12-2018, 23:42

My God, that work is impressive.
adapting that to make a pcb for the msx2 with physical z80 (including z80 & z280) would be very complicated, would not it?

Van lintweaker

Champion (457)

02-01-2019, 16:46

While waiting for the 2nd revision of my Z280 board I did some initial tests with my small Z180 adapter.
First of, MSX1,2 and 2+ just boot fine without any issues (unmodified ROMs). By default the Z180 starts with the CPU speed set to 0.5x clock speed. What MSX program can I use for speed / performance tests?

With a 14.x MHz clock (so CPU runs at 7MHz) there is the expected VPD corruption, although Space Manbow is still very playable. I'll test if setting the VDP wait function helps here.

I had no luck with any of my SD/uSD/CF card interfaces with Nextor kernel. All gave the following error:

Boot error: kernel initialization code failed, code 6

Not sure if this is due to overlapping I/O ports or timing issues.
To be continued

(note I expect the Z180 to be limited in usefullnes due to its overlapping I/O pots and lack of support for the undocumented Z80 instructions)