Control Data Cyber 170 State Hardware Reference Manual page 210

PP Programming
Inter-PP Communications
Any PP can communicate with any other PP using any channel (except the
real-time clock) by omitting the conditioning of the external devices of that
channel for a data transfer. Both single-word and block transfers can be
used. Either the sending or the receiving
PP
can activate the channel used,
after which the sending PP outputs data into the. channel register of the
channel concerned and the receiving
PP inputs data from the same register. The
transfer rate is 1 word every 250 us, except when the transfer is between PPs
in different barrels but in the same time slot. In such a case, the transfer
rate is 1 word every 500 ns. PPs that use the same time slots are as follows:
Slot PP Number
1 0, 5, 20, 25
2 1, 6, 21, 26
3 2, 7, 22, 27
4
3, 10, 23, 30
5 4,
ll,
24, 31
Software resolves priority and reservation problems arising in inter-PP
communications by interlocks stored in CM or by other means.
PP Program Timing Considerations
Some external equipment may require timing considerations in issuing function,
activate, and input instructions. Refer to the applicable external equipment
reference manual. Such timing considerations
may,
for example, be required to
ensure that the equipment attains a proper speed before data is sent (required
by some magnetic tape equipment). Also, equipment that terminates
a
data
transfer by resetting the active flag to inactive often requires timing
considerations in issuing the next function instruction.
Channel Operation
Channel Control Flags
Channel operation is affected by the channel active/inactive and full/empty
flags and, depending on the status of these two flags, the channel is said
to
be active, inactive, full, or empty. Each channel also has a marker flag for
software use and an error flag for indicating transmission parity errors.