Hi to all,
I'm trying to discover if the Saturn CPU from the HP-42S have more than the A0..A15 address lines.
I think that some non-connected CPU pins that ends on test-pads on the PCB following the sequence of the address lines (after A15) can be used as address lines for the main RAM - *IF* those pins are indeed address lines!! I don't know very deeply the Saturn processor and I don't know if its address mode is linear on the 0.5MB address area (1Mega-nibble). There is the chip-select (CS) issue also, I think that the ROM-CS and RAM-CS are hardwired on some address window. Any information on this?
I don't have a logic analyser, but I'll try to borrow a oscilloscope to peek around. If these lines can be used for addressing the RAM, the extra RAM can easily be added - 128KB maybe???
Anyway, it is easy to put 64KB of RAM in the space between $20000~$3FFFF to do some extension of its functions/OS, and if at least I can use the A15 on the normal RAM space I can put 64KB there too (128KB total).
Best regards,
Nelson