Programmable Calculators: The First Generation

[Gene]

(05-19-2017 08:17 PM)Dieter Wrote:  1975: SR52 has 20+2 data registers

1975: SR52 has card reader for recording programs and data

Dieter

Gene: Two tiny points and clarifications.

1) The SR-52 had 20 data registers (00 - 19) and it was publicized that registers 98 and 99 were also available for for regular data use, making up the 22 here. 98 and 99 had the benefit of not being cleared by the CMs command.

In addition, registers 70-97 were also available during RUN mode for STO and RCL, giving 28 more registers.

So if you are operating in RUN mode, you really have 50 data memories available.

Registers 60-69 are used for the AOS stack and under certain circumstances can be used for STO and RCL as well. This means you **could** operate in RUN mode with 60 data memories.

2) The SR-52 card reader cannot record data registers per se.

The information in point 1 above points out the trick that was used to save data registers to a program card.

Using register 98 or 99, a program loop is created that does a RCL for memories 00 - 19 and then does a STO into register 78-97. The program should fit into 64 steps (registers 70-77 are mapped into steps 00 - 63 at 8 steps per register), then you can then write a card after running the program. This card would contain the program and the rest of program memory, which contains the data registers copied into the end of program memory. The write program to a card instruction copies registers 70-97 to the card.

It turns out that the program to loop and copy data registers into program memory was **small** enough that the reverse routine ALSO fit into the program memory space 00 - 63, allowing ONE card that could save or restore data registers to / from a program card.

Very neat trick for its day.