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224
Using the I-Register for Indirect Control
B) (B5Z(@, when the number in the I-register is O through 25, de-
crements (subtracts 1 from) the contents of the primary or secondary
storage register addressed by the current numberin the I-register. In
arunning program, one step is skipped if the contents of the addressed
register are then zero.
(@, when the numberin the I-register is 0 or a positive 1 through
19, transfers execution of a running program sequentially downward
through program memory to the next label specified by the current
number in the I-register.
(@, when the number in the I-register is a negative number
between —1 and —999, transfers execution of a running program
back in program memory the number ofsteps specified by the current
negative number in the I-register.
0
(@, when the numberin the I-registeris O through 19, transfers
execution of a running program to the subroutine specified by the
current numberin the I-register. Like a normal subroutine, when a
is then encountered, execution transfers forward and continues
with the step following the
[@ instruction.
G
(@, when the number in the I-register is a negative number
between —1 and —999, transfers execution of a running program
back in program memory the numberofsteps specified by the current
negative numberin the I-register. Execution from that pointis like a
normal subroutine, so if a
instruction is then encountered,
execution is transferred once again, this time to the next instruction
after the
@.
If the numberin the I-registeris outside the specified limits when the
calculatorattempts to execute one of these operations, the display will
uses for an address only the integer portion of the numbercurrently
stored in the I-register. Thus, 25.99998785 stored in the I-register
retains its full value there, but when used as address (@, it is read
as 25 by the calculator.
In all cases using the [ (indirect) function, the HP-67
looks at only the integer portion of the current number
stored in the I-register.
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