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HP71 memory config observations
02-28-2017, 11:32 PM
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RE: HP71 memory config observations
christoph, not sure as to whether i've fully groked your findings. so, one question comes to my mind:
if there is such a single-chip 64KB RAM configured at 0x20000 (which makes sense from a configuration-routine viewpoint in order to configure all RAM in a contiguous fashion), what's going to happen if you try to read a card with the card reader? will that card overwrite the 0x2C000 window?
if yes, then i'd assume that there was never a plan to allow for 64KB single-chip RAMs, and hence trying to enable the emulator to accept such a configuration is probably a moot point anyway.

as for pulling the "DIN" on both RAMs high at the same time, i'd guess that the response to ID would lead to some "interesting" and undefined result on the bus... during its initial development phase, FRAM71 didn't have any protective bus resistors (rest assured, FRAM71(B) owners, all your modules are equipped with these). therefore, it was the strongest device on the bus and of course reliably locked down the calculator as soon as it collided with other devices on the bus. preferably with the system ROMs, that is. nevertheless, my HP-71Bs survived all these accidents. can't speak for the RAM modules, though.
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RE: HP71 memory config observations - Hans Brueggemann - 02-28-2017 11:32 PM

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