A really stupid 41C question

[Monte Dalrymple]

The HP Application Pac manuals that I have checked (Math, Navigation, Surveying) all state that the pac must be inserted into a port higher than the last Memory Module. Since Memory Modules communicate via the Data bus, while Application Pacs communicate via the ISA bus I am confused as to why there is this restriction. Anyone have some insight?

[Ángel Martin]

My (unverified) suspicion is that the MCODE logic to find the X-Mem modules installed isn't all that robust (it assumes several things as opposed to using pointers), and it will fail if the X-Mem modules are not contiguous.

I've never had to investigate this further since all my programming is for a full CX configuration (i.e. the CL as well), but the code for X-Mem control in the X-Functions module is rather complicated: the system works equally well with zero, one or two X-Mem modules and the code needs to account for all that...

But all this is weird (and probably bogus) because, as you say, communication is through the RAM device selection, and not using the ROM bus.

[Monte Dalrymple]

(07-01-2022 05:22 AM)Ángel Martin Wrote:  My (unverified) suspicion is that the MCODE logic to find the X-Mem modules installed isn't all that robust (it assumes several things as opposed to using pointers), and it will fail if the X-Mem modules are not contiguous.

I've never had to investigate this further since all my programming is for a full CX configuration (i.e. the CL as well), but the code for X-Mem control in the X-Functions module is rather complicated: the system works equally well with zero, one or two X-Mem modules and the code needs to account for all that...

But all this is weird (and probably bogus) because, as you say, communication is through the RAM device selection, and not using the ROM bus.

The restriction is talking about regular Memory Modules, not X-Mem. The only thing I can think of is that they wanted to make sure that there were no "holes" between Memory Modules?

[Didier Lachieze]

(07-01-2022 05:34 AM)Monte Dalrymple Wrote:  The restriction is talking about regular Memory Modules, not X-Mem. The only thing I can think of is that they wanted to make sure that there were no "holes" between Memory Modules?

Yes, according the HP 82106A memory module quick reference:

Quote:To be used properly, memory modules must be inserted
into the ports as specified. Memory modules must be
inserted into the ports in the port’s numeric order, from
port 1 to port 4. Do not insert modules out of order. For
example, if you insert a memory module into port 1 and
then one into port 3, there will be a gap of 64 registers
in memory.

Obviously the HP 82170A quad memory module doesn't have the same constraint, but it was released after the first Application Pacs (and before X-Mem modules):

Quote:The HP 82170A Memory Module can be inserted in
any port and provides the equivalent of four HP
82106A (64-register) memory modules. Only one HP
82170A Memory Module should be inserted in the
calculator at any time. Attempting to use any
additional memory modules in combination with the
HP 82170A Memory Module will not provide an
additional increase in memory and is not recommended
by Hewlett-Packard.

[Monte Dalrymple]

Thank you Didier and Ángel. I realized the reason shortly after my second post. It seems odd that HP would include this restriction in all of the Application Pac manuals as opposed to clarifying the Memory Module manual, but then this was pre-internet so I guess it makes sense.