IBM 1130 User Manual page 442

Console Display Lamps
Above the console printer is a panel containing a
large number of indicator lamps (or lights). These
lights indicate the internal status of the 1130 Com-
puting System. While most are of little use to the
average programmer, he does have access to one
set of lamps: the accumulator.
The accumulator is displayed as a series of 16
numbers, in four groups of four, which are either
illuminated (backlighted) or not. For example, sup-
pose the accumulator indicates the status shown be-
low, where the underlined numerals are lit:
1 0
!
2 31.1.
5 6
71
~
9
10
11
I
g
13
14
121
Since the accumulator displays a binary number,
this example means that it contains 0100 1000 1000
1001, or 18569 in decimal. An easier way to repre-
sent the number is to use the hexadecimal notation,
IBM 1131 Central Processing Unit with disk drive
Section
Subsections
Page
45
05
I
30
01
where each group of four "bits" is taken as a hexa-
decimal nu mber, obtaining 4889. (For further detail
on number systems, see Appendix A of A26-5881. )
The programmer can use the accumulator
display feature by appending a four-digit number
(from 0001 to 9999) to the FORTRAN PAUSE or
STOP statements.
If the programmer inserts a
PAUSE 3322 statement in his program, the CPU will
pause and display 3322 in the accumulator (as a
hexadecimal number) when it executes the PAUSE
statement:
1 0
.1
2
]3.1
4
§.
6
1.1
8 9
.!Q
11112 13
14 15
1
If the program contains many PAUSEs, each may
be given a different number, and the operator can
determine which PAUSE caused the CPU to halt its
operations.
This facility is useful for indicating error con-
ditions, tracing progress through a program, etc.