HP HP-15C - Section 9 Subroutines; Go To Subroutine and Return

101
Section 9
Subroutines
When the same set of instructions needs to be used at more than one point
in a program, memory space can be conserved by storing those instructions
as a single subroutine.
The Mechanics
Go To Subroutine and Return
The G (go to subroutine) instruction is executed in the same way as the
t branch, with one major difference: it establishes a pending return
condition. G label, like t label,
*
transfers program execution to the
line with the corresponding label (A to E, 0 to 9 or .0 to .9). However,
execution then continues until the first subsequent n instruction is
encountered – at which point execution transfers back to the instruction
immediately following the last G instruction, and continues on from
there.
Subroutine Execution
´bA
´b.1
G.1
|n
|n
END
RETURN
Execution transfers to line 000
and halts.
Execution transfers back to
original routine after
G.1
*
A G or t instruction followed by a letter label is an abbreviated key sequence (no ´
necessary). Abbreviated key sequences are explained on page 78.