Device Control Command Set - IBM 6400 Programmer's Reference Manual

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 format of the Acknowledge Reply data field follows:
Command Length
Command ID
Flags
Correlation Number A two byte identifier is returned if available for:
Special Data
30
6400 IPDS
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.
A two byte length
X ' D6FF ' (Acknowledge Reply)
One byte field of IPDS command stream flags
Bit 0
Bit 1
Bit 2
Bits 3-6
Bit 7
Synchronous NACKs
•
Response to information request commands
•
Acknowledgement requested (Flag byte bit 0 = 1)
•
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
Reserved
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.
Acknowledgement Continuation
Reserved
The Persistent NACK bit is for DSC Mode NACKs.
This bit has no meaning in other attachment
environments.