HP9831 operating manual

[Tony Duell]

> Tony,  have you looked at one of the 9831 OS ROMs?  Do you think it could
> be duplicated?

I don't know how much you know about the 9825/31 hardware or memory bus, 
so some of this might be obvious, but...

The memory bus is 16 bit multiplexed address and data. I can't rememebr 
the exact details, I think it's actually a 15 bit word address, with the 
other bit being used as a byte select for 8 bit writes. There are also 
come control lines.

The HP ROMs have 16 address/data pins. The address is latched internally 
_and_ they do the address decoding of the whole 15 bit (or whatever) 
address. There is no conventional chip select pin.

The system ROM cartridge contains a number of those ROMs, maybe some 
buffer chips, I forget (I do have a schematic). It would be possilble to 
read them out, but it's more work then just desodlering the chips and 
sticking them into an EPROM blower.

As regards using EPROMs to replace them (I guess that's your aim), there 
is some possible good news on that. I have 2 ROM modules for the 9825, 
the Matrix one and the Flexible Disk one. The former contains a couple of 
the HP ROM chips I just mentioned. The latter contains a couple of normal 
8-bit wide ROMs and a bit of TTL (address latch and decoder I think) to 
link them to the memory bus. Again I have schematics, so it shouldn't be 
too hard to make a sytstm ROM cartridge using standard EPROMs.

Incidentally, the later 9825s -- the ones with the ROMs on one of the 
internal PCBs -- used standed ROM chips and TTL-based interface logic.

-tony