ROM Cartridge Port PinOut

[Paul]

It's a very old trick: I use 256 memory mapped ports: from $FE00 to $FEFF. When
i want to write byte XX to the SPI interface, I make a read to the port $FEXX
and discard the result.

So this makes a second possibility. The first possibility I was hinted to was using one adress line as a "serial" line toggeling on and off to "be" the SPI bus (a second line would be needed to give the spi clock although one of these line could also be a data line).
So we are slowly gathering the required informations.

Thanks a lot dilwyn

[RWAP]

I have received some more information from Adrian Ives:

"Writing" to the ROM port requires some extra logic on the device that is being written to, but the principle is really very simple. The aborted Q-BUS project contained an API for just this purpose.



- Allocate a 256 byte page anywhere in the ROM socket addressing space. For example $FF00 to $FFFF.

- On the hardware add a decoder that catches the address range and latches the low eight bits of the address bus.

- The latched byte becomes the byte to be written to the device.



e.g. A read from $FF85 would write the byte $85 to the device.



Couldn't be easier … except … not all QLs are created equal and many of them don't implement full address decoding, so the ROM socket adress range gets repeated throughout the full address space.

[Dave]

Which is why you combine the address decoder with the ROMOE_ signal, so only in-range reads pass the filter. The ROMOE signal was well implemented on every issue of QL PCB.

That said, the exact same results can be achieved on the main expansion port more easily in the same address space, but there are 16 ranges higher in memory reserved for this too which would allow full reads/writes.

[thorsinclair]

If the main expansion port is used would it than still be possible to plug in a Gold Card? Or can SD reader circuit be added to the gold card in some way, let's say "huckepack" which would make a Mega Gold Card? What's about the disk drive connector, is this a possible way to connect the SD circuit?

[Mr_Navigator]

"Huckepack"

Wikipedia says

In transportation Piggy-back refers to transportation of goods where one transportation unit is carried on the back of something else - it is a specialised form of intermodal transportation and of combined transport. The term originated from the human practice known as 'piggybacking' where one person rides around on another's back.