Loop Control Using [Isg] - HP -11C Owner's Handbook Manual

132 Saction 9; The index Register
Loop Control Using
Example: Here is a program that illustrates how [ISG] works. It
contains a loop that pauses to display the current value in R; and
uses [ISG] to control the number of passes through the loop and the
value of a squared number. The program generates a table of
squares of even numbers from 2 through 50.
Keystrokes Display
(a\[P7R}
000-
Program mode.
(A)CLEAR (PRGM] 000-
f)(CBL){A} 001-42,21,11 Program label.
2 002- 2 } Current counter value
(nnnnn).
003- 48
004- 0
005- 5 | Counter test value (xxx).
006- ce)
iey : } Increment value (yy).
009- 4425 Store loopcontrol value in
Ry.
010-42,21, 1 Begin the loop.
011- 4525 Recall the number in Rj.
012- 4344 Take the integer portion.
013- 4231 Pause todisplay the
integer.
gf") 014- 4311 Square the number.
f)(PSE 015- 4231 Display the square of the
number.
(Afisc 016- 42 6 Increment R; by 2 and
check to see that the
counter is not greater than
the final number (50). If
the counter is greater than
the final number, skip the
next line in the program.
GTO]1 017— 22 1 Loopback to label 1.
9 ){RTN 018- 4332 Halts the program.
9 ){P/R Run mode.
~~ ew
a
wee ee YY
Section 9: The index Register 133
Now run the program by pressing [f)[A].
Keystrokes Display
A) 2.0000 When the calculator
4.0000 begins executing, it first
pauses to display the
4.0000 number to be squared,
16.0000 then pauses to display the
' square of the number.
: When the loop counter
50.0000 increments beyond 50, the
2,500.0000
program halts.
Here is what happens when you run the above program.
1, Under label [A], the number 2.05002 is stored in the I-register
as the loop control value:
annnn XXX | yw
(0000)2 050 02
Current Counter Test Increment
Value Value Value
2. Under label 1, the following sequence occurs:
After 2 and 4 (the square of 2) are displayed, the current
counter value in Ry, 00002 (nnnnn), is incremented by the
increment value 02 (yy). The new number in R; is 4.05002,
which is interpreted by your calculator as:
nnnnan XXX yy
(0000)4 050 02
Current Counter Test Increment
Value Value Value
The new counter value is then compared to the test value 050
(xxx). As the counter value has not exceeded the test value,
the calculator proceeds to the next line, [GTO] 1, and the
process is repeated with the new number.