Remote Operation
Message Exchange 5
5-9
5-14. Message Exchange
5-15. IEEE 488.2 Model
Response
Formatter
Output
Queue
Message
Exchange
Control
Input
Buffer
Parser
Execution
Control
9500 Functions
and Facilities
IEEE 488.1 bus
Input/Output Control
Bus
Messages
9500 Bus
Transmissions
General and Addressed
Bus Messages
Received
Message
Elements
Parsed
Message
Elements
Executable
Message
Elements
Response
Message
Elements
Response
Data
Requested
Bus Messages
Command
Errors
(CME bit)
Execution
Errors
(EXE bit)
Device-Dependent
Errors (DDE bit)
Query Errors
(QYE bit)
Message
Available
(MAV bit)
Status Byte
(STB)
RQS bit state
for Status Byte
Power On
(PON bit)
IEEE-488-1
Bus Interface
Filter out bus management and
configuration commands
9500B Functions
and Facilities
9500B Bus
Transmissions
gdw54.eps
Figure 5-1. IEEE 488 Message Exchange Model
The IEEE 488.2 Standard document illustrates its Message Exchange Control Interface
model at the detail level required by the device designer. Much of the information at this
level of interpretation (such as the details of the internal signal paths etc.) is transparent to
the application programmer. However, because each of the types of errors flagged in the
Event Status Register is related to a particular stage in the process, a simplified instrument
interface model can provide helpful background. This is shown below, together with brief
descriptions of the actions of its functional blocks.
5-16. Instrument STATUS Subsystem
Input/ Output Control transfers messages from the Instrument output queue to the system
bus; and conversely from the bus to either the input buffer, or other predetermined
destinations within the device interface. It receives the Status Byte from the status reporting
system, as well as the state of the Request Service bit that it imposes on bit 6 of the Status
Byte response. Bit 6 reflects the “Request Service state true” condition of the interface.
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