The Sinclair QL Forum

Hello gold card gurus!

Having managed to get my network card working with a SGC I'm wondering what the SGC and GC differences are in handling expansion cards.

SGC manual is very helpful and explains that it maps addresses $4C0000 to $4FFFFF to the expansion bus with A19 and A18 set to 1 when this access is made. The manual also has a very helpful figure showing the pin differences between SGC and non-SGC QL. Armed with this info it was relatively straightforward to get a card working.

GC manual does not have a corresponding section on expansion cards so my questions are:
- Does the GC support expansion cards?
- If it does, what are differences between GC and SGC (pins, memory mapping) ?

Many thanks in advance for any help or pointers to further documentation!

Kind regards,
Petri

ppe wrote:GC manual does not have a corresponding section on expansion cards so my questions are:
- Does the GC support expansion cards?
- If it does, what are differences between GC and SGC (pins, memory mapping) ?

If the existing schematics are to be believed A21 to A23 are not connected on the CPU, so the GC cannot be expanded, except through the ROM port.

Marcel

The gold card ties A18 and A19 to ground - so no expansion possible on this card

Thank you for confirming my suspicions, Marcel and Pr0f!

Pr0f wrote:The gold card ties A18 and A19 to ground - so no expansion possible on this card

Hi,

If A18 and A19 are disonnected from ground and connected to the QL bus, is expansion possible, or is it not that easy?

I think the problem is that the CPLD on the Gold Card just doesn't have these outputs - so they have no meaning, and the CPU's address lines are used by that CPLD to drive the RAM and select any necessary QL addresses in the lower 256K (an un-expanded QL) when required for I/O and screen etc.

The SGC does drive these lines, but together - effectively translating what was 0x0C0000 to above the 4M of memory limit. I presume they patched ROM scan code to look for I/O at higher addresses.