RCA 70/46 Reference Manual page 80

Block 14
Block 15
Input/Output Operation
• A test is made to see if the service request was honored for a device
on the multiplexor channel. If it was not, program control continues with
the next instruction or with the instruction that was interrupted due to the
service request.
• If the service request was honored for a device on the multiplexor
channel, a test is made to see if it is a burst mode operation. If it is not a
burst mode operation, the sub-channel registers are sent back to non-
addressable main memory. In either case, program control continues with
the next instruction or with the instruction that was interrupted due to
the service request.
Notes on Servicing a Data Transfer:
1. All input/output data service requests are honored depending on
the channel's position in the priority sequence.
2. The following tests occur when a data byte is transferred to main
memory:
a. The main memory address to which the data byte is to be trans-
ferred is tested to see if it is in a memory protected area (Memory
Protect feature must, be installed). If it is, the protection check
bit in the channel status byte is set (no data transfer occurs)
and the device control electronics is told to set an end condition
on the next data service request (see Block 13).
b. The main memory address to which the data byte is to be trans-
ferred is tested to see if it is in available main memory for the
system. If it is not, the program check bit in the channel status
byte is set (no data transfer occurs) and the device control
electronics is told to set an end condition on the next data service
request (see Block 13).
3. The following tests occur when a data byte is transferred from
main memory:
a. The main memory address from which the data byte is to be
transferred is tested to see if it is in available main memory for
the system. If it is not, the program check bit in the channel
status byte is set (no data transfer occurs) and the device control
electronics is told to set an end condition on the next data service
request (see Block 13).
b. The data byte to be transferred is checked for correct parity.
If parity is not correct, the data check bit in the channel status
byte is set and the device control electronics is told to set an end
condition on the next data service request (see Block 13).
4. If a main memory parity error occurs while fetching the subchannel
registers, the channel control check bit in the channel status byte
is set, and the device control electronics is told to set an end condition
on the next data service request (see Block 13).
5. If a scratch-pad memory parity error occurs during the servicing
of a data transfer, the channel control check bit in the channel
status byte is set and the device control electronics is told to set
an end condition on the next data service request (see Block 13).
71