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Channel Interface
7942 and 7946
TRANSACTION
PHASE
CO~MAND
EXECUTION
REPORTING
CHANNEL
ACTIVITY
Q
COMMAND MESSAGE
(0
EXECUTION MESSAGE
REQUEST
(IF APPLICABLE)
G
A
EXECUTION
MESSAGE
'I
(IF APPLICABLE)
@
REPORTING MESSAGE
REQUEST
@
.A
REPORTING
MESSAGE
'It
UNIT OPERATING
STATE
CD
COMMAND-READY
@
ACCEPT AND VALIDATE COMMAND
NOTE: LOGICAL
~HINE
GOES TO REPORTING
STATE
12
IF COMMAND IS INVALID. OR
IF HOST REQUESTS REPORllNG MESSAGE.
o
BEGIN EXECUTION OF COMMAND
@
REQUEST EXECUTION MESSAGE (IF APPLICABLE)
(1)
CO~PLETE
EXECUTION OF COMMAND
~SEND
DATA.
RECIEVE DATA. OR ACCOMPLISH COM AND ACTION)
G
COMPUTE TRANSACTION STATUS
@
REQUEST REPORTING MESSAGE
@
SEND ONE-BYTE REPORT (QSTAT)
(1)
Logical Machine idle in command -ready state.
(2)
Host sends command message.
(3)
Logical Machine accepts and verifies command. If command is valid, Logical Machine moves
to execution state. If not, Logical Machine moves to reporting state.
(4)
Unit begins execution of command.
(5,6) If command involves data transfer, Logical Machine requests an execution message. If not,
unit completes execution (6).
(7)
Execution message is established if command involves a data transfer.
(8)
Unit completes execution of command. If command involves data transfer, unit sends or
receives data through channel module. If not, unit completes action called for in command
message.
(9)
Logical Machine computes completion status of transaction.
Pass/Fail status
IS
set into
QST AT, complete status set into request status.
(10,11) Logical Machine requests reporting message.
(12)
Reporting message is established.
(1
3)
Logical Machine sends 1 - byte reporting message (QST A T) indicating Pass/Fail status of trans-
action. Host must send request command for complete status report
(20
bytes).
Figure 2 -1. Transaction Structure
2-10
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