Control Data Cyber 170 State Hardware Reference Manual page 167

PP InputlOutput Instructions
Input to
A
from channel d
IAN d
This instruction transfers a word from input channel d to the lower 12 bits of
the
A
register. The upper 6 bits of A are cleared to 0.
NOTE
If bit 5 of d is clear and the channel is
inactive, this instruction hangs the PP,
waiting for the channel to go active and full,
if executed. If bit 5 of d is set and the
channel is inactive or is deactivated before a
full is received, the instruction exits. The
word is not accepted, and the
A
register clears.
Input
A
words to m from channel d IAM m,d
This instruction transfers a block of 12-bit words from input channel d to
PPM.
The first word goes to the
PPM
address specified by m.
The A register
holds the block length.
A reduces by 1 as each word is read. The input
operation completes when A equals 0 or the data channel becomes inactive. If
the operation terminates by the channel becoming inactive, the next storage
location in PPM is set to 0. However, the word count is not affected by this
empty word.
Therefore, A holds the block length minus the number of real data
words read.
During this instruction, address 0000 temporarily holds P while m
is
held in
the
P
register. P advances by 1 to hold the address for the next word as each
word is stored.
NOTE
I f this instruction executes when the data
channel is inactive, no input operation is
accomplished, and the program continues at
P
plus 2. However, the location specified by
rn
is set to 0.