PokeMon wrote:I am not sure for the Lambda, but the Sinclair ZX80 and ZX81 have the dataline (databus) not directly wired from the CPU but from the RAMs. There are resistors decoupling the (external) RAM content when the ULA becomes active during video display and takes the opcode from the (external) RAM and serves a NOP to the CPU instead. So there are resistors between RAM and ROM databus to the CPU databus. Only the ULA is connected directly to the databus. The address bus is taken directly from the CPU for ZX80 and ZX81.
As far as I know, the Lambda is compatible to ZX80 and ZX81. So if you want to have a compatible expansion slot it is maybe recommandable to use the datalines or RAM, decoubled via resistors from CPU instead of CPU lines directly.
Thanks for the explanation, from the schematics I've seen I couldn't make out where the expansion connects into the lines. I'll have to open up a lambda, trace out the expansion and see how things are laid out, but a total ZX compatible rework of the expansion is probably beyond me. At very least I'm looking to return the missing INT, NMI, HALT, BUSACK, WAIT, BUSRQ, RESET & MI lines to the connector.
gozzo wrote:these may be of use...(many apologies if I am breaching any copyright, but I found these freely on the 'net) . I know it says 'Power 3000' but it's supposedly identical to the Lambda!
Yes, it's the closest thing I've been able to locate as well... at some point I should spend some time poking around inside the Lambda and see.