Control Data Cyber 170 State Hardware Reference Manual page 154

PP Replace lnstructions
Replace Subtract
37 d Replace subtract 1 (d)
SOD d
This instruction replaces the quantity at location d with its original value
minus 1 . The result remains in the A register at the end of the operation, and
the original content of A is destroyed.
47d
Replace subtract 1 ( ( d ) )
This instruction replaces the operand, which is obtained from the location
specified by the content at location d, by its original value minus 1 . The
result remains in the
A
register at the end of the operation, and the original
content of
A
is destroyed.
57dm Replace subtract 1 (m
+
( d ) ) SOM m,d
This instruction replaces the operand, which is obtained from the location
determined by indexed direct addressing, by its original value minus 1. The
result remains in the A register at the end of the operation, and the original
content of A is destroyed.
In indexed direct addressing, the quantity m, which is read from PPM location
P
plus 1, serves as the base operand address to which the content o f d is added.
If d equals 0, the operand address is m, but if
d is not equal to 0, m plus the
content in d is the operand address. Therefore, location d may be used as
an
index quantity to modify operand addresses.