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Dave Frederickson · (This post was last modified: 12-18-2021 02:28 PM by Dave Frederickson.)

(12-18-2021 10:58 AM)Hans Brueggemann Wrote: the HP-71B declares/recognizes a freed port by the "3BDDDDDE" in that particular port's header. an attempt to claim that port back into main memory will fail if that header is not found. this can happen when F_addresses are accidentally being swapped or when jumper CN2-2 is set. to hunt down the freed port in question, a PEEK$ (Port_begin_H_adr$, 16) done on each of the RAM modules' start address should reveal the port. however, the situation is a bit tricky here, because of E4 being only 16 kB. so, this is my best guess on how the HP-71B would arrange the memory:

Code:

H_0x30000: 18 H_0x40000: 19 H_0x50000: 1A H_0x60000: 9B H_0x70000: E4
it is also a good idea to experimentally configure the unused F_Blocks as additional RAM and then check them individually for IRAM headers.

Be aware, the Finance ROM contains the IRAM identifier even though it's a ROM.

According to the IDS, the IRAM identifier is B3DDDDDE and a hex editor will show it with the nibbles reversed as 3BDDDDED. (Was there something wrong with DEAD BEEF or CAFE BABE?)