CMT 64Kb RAM module for HP-71b question

[J-F Garnier]

(10-11-2021 07:33 PM)Sylvain Cote Wrote:  MULTIMOD with three external 32KB RAM memory module

Code:

power off
insert third external 32KB RAM memory module
power on → normal
MEM → 113543   (with MEMBUF)
power off
power on → memory lost
MEM → 115049   (without MEMBUF)
power off

Code:

loop
  power on → normal
  MEM → 98665
  power off
  power on → normal
  MEM → 115049
  power off
end-loop

Ok, I may have the beginning of an explanation.
It seems to me that once the Multimod configures a 16K ROM at 80000, then this ROM is not correctly unconfigured at the next configuration, and interfere with the configuration that uses the absolute address 80000 for RAM/IRAM check..
After this incorrect configuration, the 16K ROM is no more at 80000 and next config will pass correctly (putting the 16K ROM again at 80000), the next one will fail again. And so forth.

A Multimod port becomes configured at 80000 if:
- it is a 16K ROM (32K ROM are configured from D0000 downward),
- addresses 3xxxx to 7xxxx are occupied by other MAIN RAM (or other 16K ROM).

Mark may confirm if there is a problem with port unconfiguration (RESET opcode).

J-F