Device Control Command Set
However, sometimes the printer will not return a correlation ID, even if every
command has a correlation ID.
The maximum length of this command is 255 bytes. If there is a five-byte
command header (no correlation ID present), the data field can be up to 250
bytes long. If a correlation ID is present in the header, the maximum data field
length is 248 bytes. The Acknowledge Reply data field contains the
acknowledgment type, page/copy counters, and a Special Data (SD) area. The
printer loads the Special Data area with the appropriate data when one of the
following occurs:
•
The printer receives one of the following information request commands:
- Sense Type and Model
- Obtain Printer Characteristics
- Request Resource List.
•
An error occurs. Under this condition, the printer loads the special data area
with the sense bytes and sends a negative acknowledgment (NACK) to the
host.
The format of the Acknowledge Reply data field follows:
Com mand Length A two byte length
Command ID X
'D6FF' (Acknowledge Reply)
Flags One byte field of IPDS command stream flags
Bit 0 Reserved
Bit 1 Correlation Number Present
The printer receives a command with this bit set,
and then returns the Acknowledge Reply also with
this bit set to indicate that a two-byte “Correlation
Number” follows.
Bit 2 Acknowledgement Continuation
Bits 3-6 Reserved
Bit 7 The Persistent NACK bit is for DSC Mode NACKs.
This bit has no meaning in other attachment
environments.
Correlation Number A two byte identifier is returned if available for:
•
Synchronous NACKs
•
Response to information request commands
•
Acknowledgement requested (Flag byte bit 0 = 1)
Special Data The Special Data area of the Acknowledgement Reply
contains:
•
Error sense bytes when reporting an exception.
•
Response to the following information request
commands:
- “Sense Type and Model (STM)” on page 42
- “Obtain Printer Characteristics (OPC)” on page 52
- “Request Resource List (RRL)” on page 47
30 6400 IPDS
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