IPDS for Control Units
3270 IPDS Query Reply structured field
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This query reply structured field (with a Q code of 9A) indicates IPDS is valid
in DSC mode. In addition, this query reply also specifies the maximum
outbound transmission size that is allowable.
IPDS Application in LU-1 Mode
An application program can switch the printer from SCS to IPDS during an LU-1
session. The IPDS data stream is carried in the IPDS structured fields and is
processed entirely by the printer.
Determining IPDS Capability
An application can determine the IPDS capability of a printer operating in LU-1
mode by issuing a Read Partition query or a Read Partition Query List structured
field. The query list, if used, should contain a Q code of X
'A2' (data streams).
The printer returns a data stream query reply structured field containing a data
stream identifier indicating IPDS (X
'02'). This IPDS identifier is in addition to
(and following) the base data stream identifier of SCS (X
'00').
Both the read partition query (or query list) structured field and the query reply
structured field are sent in a chain that begins with a function management
header (FMH) of one. This header contains a destination select of Begin/End
(DESSEL equals BEDS) along with a data stream profile of Structured Fields (DSP
equals SF).
An FMH-1 that precedes a read partition query or query list has the following
format:
0601000B6000
An FMH-1 that precedes a query reply has the following format:
0601008B6000
Inbound Structured Fields
When the printer is in LU-1 SCS mode, the query reply and the save are the only
structured fields sent inbound. These fields are preceded with an FMH.
When the printer is in LU-1 mode with IPDS, an IPDS acknowledge reply is the
only structured field sent inbound. This field that the printer sends without an
FMH can be a STM, an OPC, an ACK, or a NACK.
It is also possible for the control unit to receive a solicited or unsolicited
acknowledgment (ACK/NACK) reply from the printer when in LU-1 IPDS mode.
When a NACK occurs, the information must be received after a change direction
to allow data to flow inbound to the control unit.
170 6400 IPDS
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