IPDS for Control Units
Abnormal Termination of Printer Operation
Any of the following causes rejection of the transmission with a sense equals op
check and cause the control unit to send an abort to the addressed printer:
•
Receipt of a data chain structured field indicating continue or end when not
in chain state
•
Receipt of a data chain structured field indicating begin when already in
chain state
•
Receipt of any 3270 command except BSC Copy, Write Structured Field,
Erase Write (WCC equals Reset), or Erase Write Alternate (WCC equals
Reset) when in the chain state
•
Receipt of a Write Structured Field command that does not contain a data
chain structured field when in the chain state.
Copy Considerations
The printer is not available for an operator-initiated copy operation when in IPDS
mode.
If a BSC Copy command is received when in IPDS mode, IPDS mode terminates
and the BSC Copy operation occurs.
Note: It is required that an unordered page be contained within a chain.
Chaining and Error Recovery in 3270 IPDS Mode
A chain is a unit of error recovery. At the end of the chain, the printer delays
sending operation-complete to the control unit until all the received data prints.
To make certain that all deferred printing completes, a chain of IPDS structured
fields should end in the home state. The printer forces IPDS into the home state,
if necessary, to force deferred printing to occur when a chain terminates.
If chaining is not used, each transmission should end in the home state. If
necessary, the printer forces entry into the home state.
IPDS ACK/NACK Sequence in DSC Mode (Channel-Attached)
When using IPDS print operations, the printer can have inbound ACK/NACK data
to send to the host application. Inbound data may result from an Acknowledge
Request required by a prior outbound transmission or from an error condition to
be reported.
Not Recommended NACK Sequence for Printers
When the printer operates in the DSC (channel-attached) mode with IPDS, and
the printer has inbound data to send, the following sequence is not
recommended:
1. The host application receives an Attention from the printer notifying the
application that inbound data is available.
2. The host application issues a Read Modified to the printer.
3. The printer sends the NACK to the host application.
4. The host application issues an Erase/Write WCC equals Reset to the printer.
This ends IPDS mode.
Appendix B. Summary of IPDS for Control Units 181
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