10-18 Status Structure Model 6485 Picoammeter Instruction Manual
Programming example — program and read registers
This command sequence programs and reads the measurement registers. Registers are
read using the binary format (which directly indicates which bits are set). The command to
select format (FORMat:SREGister) is documented in Table 10-2.
FORM:SREG BIN ' Select binary format to read
' registers.
STAT:MEAS:ENAB 512 ' Enable BFL (buffer full).
STAT:MEAS:COND? ' Read Measurement Condition Register.
STAT:MEAS? ' Read Measurement Event Register.
Queues
Model 6485 uses two queues which are first-in, first-out (FIFO) registers:
• Output queue — Used to hold reading and response messages.
• Error queue — Used to hold error and status messages.
Model 6485 status model (Figure 10-1) shows how the two queues are structured with the
other registers.
Output queue
The output queue holds data that pertains to the normal operation of the instrument. For
example, when a query command is sent, the response message is placed in the output
queue.
When data is placed in the output queue, the message available (MAV) bit in the status
byte register sets. A data message is cleared from the output queue when it is read. The
output queue is considered cleared when it is empty. An empty output queue clears the
MAV bit in the status byte register.
A message is read from the output queue by addressing Model 6485 to talk after the
appropriate query is sent.
Error queue
The error queue holds error and status messages. When an error or status event occurs, a
message that defines the error/status is placed in the error queue.
When a message is placed in the error queue, the error available (EAV) bit in the status
byte register is set. An error/status message is cleared from the error queue when it is read.
The error queue is considered cleared when it is empty. An empty error queue clears the
EAV bit in the status byte register.
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