HP-48G(X) Port Addressing


I've successfully upgraded two HP-48G's to 256K memory, using two 128K chips each, thus providing each with 128K "user" memory, and 128K as Port 1.

I'm hoping to go further. A question I have is re: naming and addressing the (up to) 32 ports available as 4Mb in Card Slot 2. The HP 48G Series User's Guide says (p. 28-2, "Card Slot 2") that one may install "4096 KBytes, of which only 3968 are accessible." Further, it gives examples: "a 1-MByte plug-in card offers Ports 2 through 9 ... A 4-MByte plug-in card offers Ports 2 through 32."

Are the first two "ports" ostensibly available via Card Slot 2 (Ports 0 & 1) actually covered by user memory and the port in Card Slot 1? (User memory and Port/Card Slot 1 each have dedicated chip select lines.) How do the Card Slot 2 port numbers and hardware address signals used during bank switching (as discussed in Matthew Mastracci's "Guide to the Saturn Processor", sec. 4.4) relate to the port names ("Port 2", etc.) mentioned in the User's Guide?

The memory map in James Donnelly's book is inconclusive, and elsewhere (I think in the HP-48 FAQ) I found reference to a "Port 33"!!??

If anyone can help with an answer or point me to other sources, I'd greatly appreciate it.

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