Section 13: Indirect Operations198
FS? g nn   ‘‘Flag set’’ test.
FC? g nn   ‘‘Flag clear’’ test.
FS?C g nn   ‘‘Flag set’’ test and clear.
FC?C g nn   ‘‘Flag clear’’ test and clear.
X<> g nn   Exchange X and any register.
CATALOG g nn   Catalog List.
To use an indirect address with a function, first store the desired register address number (the indirect address) in the register you are using for indirect control. Then execute the function and press g and specify the indirect address. When you press g , the HP-41C prompts you for the indirect address. Indirect addressing will become more clear as you read on in this section.
You can indirectly address any of the primary storage registers or extended storage registers (if your HP-41C has been extended with additional memory modules) currently allocated in the HP-41C. Remember, you can allocate up to 64 primary storage registers on your basic HP-41C. When you extend the HP-41C memory with plug-in-memory modules, the storage register capacity of the calculator is increased. All extended registers (R(100) through R(318)) require the use of indirect addressing.
If the indirect or direct register address is outside the limits of the current allocation or the number of registers in the HP-41C, the display will show NONEXISTENT. In all cases only the absolute value of the integer portion of the register address is used by the calculator.
Indirect Store and Recall
To store and recall numbers indirectly using any of the primary or extended storage registers, simply press STO or RCL , g , and specify the indirect address. By changing the register address number, you can change the address specified by the function.
You can easily demonstrate how indirect store and recall work by using the HP-41C manually. For example, to store the number 2.54 into R10 using R02 as an indirect address register:
Keystrokes Display    
10 STO 02
  First store the desired register address (R10) into the indirect address register (R02).
  2.54 _    
  The number.
STO g 
  STO IND _ _    
  Notice how the HP-41C prompts you for the indirect address.
  The number 2.5400 is now stored into register R10.