HP-34C Single Use I Register

[Matt Agajanian]

Hi all.

It would seem that since the I Register is used for DSE & ISG operations, using the I register for other indirect functions/operations is not possible.

Or, have you figured out a way to use the I register for other purposes if you’re using DSE or ISG as well?

[Gene]

Correct. Not at the same time.

Same as for the HP-67/97's I register. If you are using it for looping, you can't use it for something else unless the value used in looping is used to address memories or such. To load memories 1 - 9 the I register could be used to loop and store the value indirectly.

Any machine with a single I register would face the same chokepoint at the single I register - you can't loop from 1 to 9 and also be storing the values into the odd registers without manipulating the value in I since there is only the one register.

The HP-41 of course could use any register, but not the 67/97, 34C, 29C, etc.

[Joe Horn]

The HP 35s uses its I and J variables as indirect registers, thus allowing STO(I) and STO(J)... but no other variables can be used indirectly like that. Is the 35s the only HP model with exactly two indirect registers?

[Paul Dale]

It is possible to swap the I register for another to get double use. It's consumes lots of extra steps though.

[Gene]

True. RCL I RCL 00 STO I X<>Y STO 00 to swap another value into I and save the previous value (a similar sequence would be needed to put it back)...

using 00 to stand for any register.

Similar things had to be done on the SR-52 when the TI designers used memory 00 for all sorts of things.

[Didier Lachieze]

(08-15-2022 01:41 PM)Gene Wrote:  True. RCL I RCL 00 STO I X<>Y STO 00 to swap another value into I and save the previous value (a similar sequence would be needed to put it back)…

Or, shorter : RCL 00 X<>I STO 00

[Gene]

Oops. Forgot about that and it's right on the keyboard. :-)
Gene

[RMollov]

Can you park another car in a garage, where there is a car parked already?

[Massimo Gnerucci]

(08-16-2022 09:18 AM)RMollov Wrote:  Can you park another car in a garage, where there is a car parked already?

Sure!

[ctrclckws]

Two beautiful machinas.