I think it may be possible, despite delays. The YM goes tri-state whenever there is invalid address on the high bits (i.e. different from %0000xxxx) Scenario: The 68k sets bdir & bc1 & address %0001xxxx YM0 ignores this, as address is not 0000 YM1, because of delay on the D4 line, also sees ...

The bootsector is the smallest thing you can have. 512 bytes. Minus several bytes to make it a valid disk and bootable. That leaves you officially with 452 bytes available. But you can squeeze up to 484 bytes if you know exactly what TOS does with that data. Additional info: I found a more recent ve...

I made a life using "grafics"-operations, but with the CPU. It's nicely fast and small (it fits in a boot sector). I got that idea from someone who did life with blitter on the Amiga. As you also found out, you only need to count to 4. It is a reimplementation of an adder logic chip by usi...

As expected, the simulation is not powerful enough to make an analog switch work correctly. It keeps tri-state and active signal sticking on the same bus segment. But well, I get the idea and it should work. https://circuitverse.org/simulator/edit/34126 Circuit is simple and small. If I find for all...

I will try to implement the method of the analog switch in the sim. Addressing the YM: using additional registers on the same addresses has the advantage to also work on falcon (which bus errors an everything outside of ff8800-ff8803). Also some demos use other shadow registers so you can't put an Y...

Or maybe the YM does this too, i.e. it knows it was not addressed by the previous address bus cycle, and so ignores the next data bus cycle. At least that's how I interpret the text. You address a supposedly differently that 0000 coded YM, and then just write data on the bus, and that YM takes the d...

Nice, thanks. You are well better in circuitry than me. That online simulator does really not like tri-state bus setups. No idea if it works for you: https://circuitverse.org/simulator/embed/34126 Don't you need to memorize which chip got selected (i.e. having that latch somewhere) so when you do re...

Hi interesting if the high address bits are not 0 that the YM does not give any data. So I tested this on real hardware, and indeed, I cannot read back a value written if the bit 4 is set. Also hatari emulates this correctly. I read back 255 And trying to write does not work (the previeous register ...

Edit But after reading Gunstick's method of latching bit 4 of the data written to register select (ie. D12 when BDIR is write and the address is $FFF8800) sounds awesome to me. Extending that to latching D12,D13,D14, and D15 would allow in theory up to 16 YM chips on the same address space(!!) (Tha...

Meanwhile my logic simulator is half-fully featured. But it bugs a bit, because I tried to use a bidirectional data bus in a software which does not like stuff like that. So the "read data" operation, which is rarely used, is disabled. I just deleted those connections (was a kludge anyway)...