Compuprint 4247-Z03 Programmer Manual - Manual (Page 100)

IPDS Command Format
All of the printer commands use the following format:
Length Command Flag Correlation ID Data
Note: Bit numbering follows the EBCDIC convention with bit zero being the most significant bit. A
description of each field follows.
Length
Length is a two-byte field that specifies the length of this command. This count includes the two-byte
length field, the command field, the flag byte, and the optional fields (Correlation ID and Data Fields). The
Length field can be any value from 5 to 32,767 (X'7FFF').
Command
Command is a two-byte field that specifies the IPDS command code. See Table 1 on page 81 for a list of
valid command codes.
Flag
Flag is a one-byte field that contains the IPDS command stream flags.
Bit 0 of this byte is the Acknowledgment Required (ARQ) flag. If this bit is on, the host requests the printer
to send an Acknowledge Reply.
Bit 1 of this byte is the Correlation ID flag. If this bit is B'1', a two-byte correlation number follows this flag
byte. If this bit is B'0', the optional correlation number is not present and the following byte or bytes contain
the data field.
Bit 2 of this byte is the acknowledgement continuation flag. If this bit is B'1', the host is requesting
continuation of the current Acknowledge Reply. If this bit is B'0', the host is not requesting continuation.
Bits 3-7 of the flag byte are reserved and must be zero.
Correlation ID
Correlation ID is a two-byte value that specifies an identifier for this command. The Correlation ID is an
optional field and is only present if bit 1 of the flag byte is B'1'. The printer can use any value between
0000 and FFFF for this ID. If an error occurs on a command prior to acceptance for processing, the printer
sends a negative acknowledgement (NACK) to the host. If the printer recognizes the command that
caused the error, the Correlation ID field in the NACK will contain the ID of the command responsible for
the NACK. Correlation ID is also returned in response to commands that request information and
commands that request an acknowledgement.
Data
80 Programmer Manual