Section 7: Simple Programming117
When a program line contains an instruction whose name is too long to display all at one time, the HP-41C ‘‘scrolls’’ the information through the display. section 8 shows how SST and BST can be used to view these program lines.
The Basic HP-41C and Initial Configuration
The HP-41C comes standard with 63 registers. Initially, the HP-41C allocates 17 of these to data storage registers and the remainder (46) to program memory.
Changing Memory Allocations
If at any time you fill program memory with programs and attempt to load more instructions, the HP-41C will pack program memory and display TRY AGAIN (more about packing later). When program memory is full, each time you attempt to load an instruction the calculator packs program memory and again displays TRY AGAIN . By executing SIZE (size of data register allocation) you can change the number of registers that are allocated to program memory and data storage registers to make room for more program instructions (or to change the number of data storage register).
When you execute SIZE , the HP-41C prompts you for a three-digit number from 000 through 318. SIZE specifies the total number of registers allocated to data storage registers only. When you change the data storage register allocation, the number of registers in program memory is automatically changed. If you increase the storage register allocation, the number of registers in program memory decreases; if you decrease the number of data storage registers, the number of registers in program memory automatically increases.
Note that if you execute SIZE and attempt to decrease the number of registers in program memory when those registers contain program instructions, the HP-41C will pack program memory and display TRY AGAIN . Before you can change program memory into data storage registers, you must clear enough program instructions out of program memory to make room for the reallocation. This prevents you from accidentally losing program instructions when you execute SIZE .
For example, if you change the number of data storage registers from 17 to 21, program memory automatically decreases in size. You are adding four registers to data storage registers, and that decreases the number of registers allocated to program memory by four. Note that data storage registers are numbered 000-318. So SIZE 017 allocates R00 through R16 to data storage registers.
  Initial Allocation   New Allocation  
  Data Storage   Registers in   Data Storage   Registers in  
  Registers   Program Memory   Registers   Program Memory  
  17   46   21   42  
  (R00 through R16)       (R00 through R20)      
Each register you add as a data storage register removes one register from program memory, and each register you remove from the data storage registers adds one register to program memory.