IPDS for Control Units
Figure 39. Synchronous ACK/NACK in DSC (Channel-Attached) Mode
Note: At the end of this sequence, the printer is still in IPDS mode. The printer
does not send the ACK/NACK to the host.
IPDS ACK/NACK Sequence in DSC Mode (BSC-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.
The first NACK sequence discussed below for use with printer is not desirable.
The second NACK sequence for use with printer is recommended.
Not Recommended NACK Sequence for Printers in DSC Mode
(BSC-A tta c h ed )
When the printer operates in the DSC (BSC-Attached) mode with IPDS and the
printer has inbound data to send, the following is the recommended sequence:
1. The host application polls the printer.
2. The printer returns Device End to the host as a response to the poll.
3. The host application responds to the Device End with an acknowledgment.
4. The printer responds to the acknowledgment by sending the NACK to the
host application.
5. The host application responds to the NACK by sending another
acknowledgment.
6. The printer sends an End of Transmission to the host.
186 6400 IPDS
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