Chapter 10. Self-Check Feature; Computing The Self-Check Digit; Modulus 10 - IBM 3742 Reference Manual

Chapter 10. Self-Check Feature
The self-check feature provides a method for checking the
entry in numeric fields that contain a precomputed self-
check digit. The self-check digit is the last digit in the field,
and has been precomputed by using either of two
algorithms, modulus 10 or modulus 11.
Self-check fields are specified in the program by the use of
the following characters:
H Modulus 10
C Modulus 11
F Modulus 10 skip
G
Modulus
11
skip
L Modulus 10 dup
M- Modulus 11 dup
Fields defined by the characters F and G act as skip fields
when the AUTO/OUP/SKIP switch is on and as manual
self-check fields when the AUTO/OUP/SKIP switch is off.
Fields defined by the characters Land M act as dup fields
when the AUTO/OUP/SKI P switch is on and as manual
self-check fields when it is off.
When dup or skip and self-check are combined in a field,
the self-check is performed after the auto function. If a
self-check error is found, turn off the AUTO/OUP/SKIP
switch to backspace, and correct the self-check number.
Blank fields check correctly in the enter mode, but cause a
C error in verify mode. This allows a self-check field to be
skipped in enter mode and entered later in verify mode.
Numerals 0 through 9 and all other characters with the
values 0 through 9 in the low-order hex digit are totaled
by the low-order hex digit value. All other characters are
totaled as the value zero·.
If self-check errors occur, three methods of error recovery
are:
1.
Press RESET to unlock the keyboard and remove the
error condition. This permits entry of a new charac-
ter or backspacing to correct a preceding character.
2.
Press the dash key with either shift key to (a) remove
error condition, (b) overscore the units position with
the high order hex 0, and (c)
e~it
from the field.
3. Press NUM SH I FT and the & key to (a) remove error
condition, (b) overscore the units position with the
high order hex C, and (c) exit from self-check field.
COMPUTING THE SELF-CHECK DIGIT
Modulus 10
Modulus 10 can be computed for any number from 2 to
127 digits long. To compute modulus 10, do the following:
1.
2.
3.
Multiply the units position and every alternate position
of the basic number, excluding the self-check digit,
by 2.
Add the digits in the products to the digits in the
basic number that were not multiplied.
Subtract the sum from the next higher number
ending in zero.
The difference is the self-check digit.