10-2
Status Structure
Model 6487 Reference Manual
Overview
The Model 6487 provides a series of status registers and queues allowing the operator to
monitor and manipulate the various instrument events. The status structure is shown in
. The heart of the status structure is the status byte register. This register can be
read by the user’s test program to determine if a service request (SRQ) has occurred and
what event caused it.
Status byte and SRQ
— The status byte register receives the summary bits of four status
register sets and two queues. The register sets and queues monitor the various instrument
events. When an enabled event occurs, it sets a summary bit in the status byte register.
When a summary bit of the status byte is set and its corresponding enable bit is set (as pro-
grammed by the user), the RQS/MSS bit will set to indicate that an SRQ has occurred.
Status register sets
— A typical status register set is made up of a condition register, an
event register, and an event enable register. A condition register is a read-only register that
constantly updates to reflect the present operating conditions of the instrument.
When an event occurs, the appropriate event register bit sets to 1. The bit remains latched
to 1 until the register is reset. When an event register bit is set and its corresponding enable
bit is set (as programmed by the user), the output (summary) of the register will set to 1,
which in turn sets the summary bit of the status byte register.
Queues
— The Model 6487 uses an output queue and an error queue. The response mes-
sages to query commands are placed in the output queue. As various programming errors
and status messages occur, they are placed in the error queue. When a queue contains data,
it sets the appropriate summary bit of the status byte register.
