User`s guide

A: BSC 3270 Line Control Procedures
DC 900-1340I 205
combinations of status and sense bits, only a portion of this total is normally used.
These combinations are listed in Figure 4–9 of the 3274 Control Unit Description and
Programmer’s Guide, IBM. A tributary link of the ICP can maintain any of the combina-
tions of sense and status bits shown in Tab le A –1.
Normally, The ICP sends any pending status to the BSC 3270 master in response to a
specific poll. There are some instances where pending status is sent in response to the
next general poll. These instances involve changes in 3270 virtual device status condi-
tions. Ta ble A –2 lists the status condition changes that cause a status message to be gen-
erated in response to a general poll.
Table A– 1: Sense/Status Bit Combinations
Sense/Status
Bits
Description
CR An invalid or illegal 3270 command is received.
OC An invalid command sequence is received (ESC is not the second data character).
IR The addressed device is unavailable
IR, DE A device that was previously recorded as ready, available, and busy is now not
ready and not busy.
DB The addressed device is busy.
DB, US A write or copy command was directed to a busy device.
DE A device previously recorded as busy is now not busy, or a device previously
recorded as unavailable is now available.
Table A– 2: Condition Changes that Generate Responses to General Polls
Device Condition Change Status Bits Set
Non-existent to available DE
Unavailable to available DE
Busy to available DE
Busy to unavailable IR, DE