6-30
Remote Programming
STATUS BYTE DEFINITIONS
The SR850 reports on its status by means of four status bytes: the Serial Poll Status byte, the Standard Event
Status byte, the LIA Status byte, and the Error Status byte.
The status bits are set to 1 when the event or state described in the tables below has occurred or is present.
SERIAL POLL bit name usage
STATUS BYTE 0 SCN No scan in progress (Stop or Done). A Paused
scan is considered to be in progress.
1 IFC No command execution in progress.
2 ERR An enabled bit in the error status byte has been
set.
3 LIA An enabled bit in the LIA status byte has been
set.
4 MAV The interface output buffer is non-empty.
5 ESB An enabled bit in the standard status byte has
been set.
6 SRQ SRQ (service request) has occurred.
7 Unused
The ERR, LIA, and ESB bits are set whenever any bit in both their respective status bytes AND enable regis-
ters is set. Use the ✳SRE, ✳ESE, ERRE and LIAE commands to set enable register bits. The ERR, LIA and
ESB bits are not cleared until ALL enabled status bits in the Error, LIA and Standard Event status bytes are
cleared (by reading the status bytes or using ✳CLS).
Using ✳STB? to read the Serial Poll Status Byte
A bit in the Serial Poll status byte is NOT cleared by reading the status byte using ✳STB?. The bit stays set
as long as the status condition exists. This is true even for SRQ. SRQ will be set whenever the same bit in the
serial poll status byte AND enable register is set. This is independent of whether a serial poll has occurred to
clear the service request.
Using SERIAL POLL
Except for SRQ, a bit in the Serial Poll status byte is NOT cleared by polling the status byte. When reading
the status byte using a serial poll, the SRQ bit signals that the SR850 is requesting service. The SRQ bit will
be set (1) the first time the SR850 is polled following a service request. The serial poll automatically clears the
service request. Subsequent serial polls will return SRQ cleared (0) until another service request occurs.
Polling the status byte and reading it with ✳STB? can return different values for SRQ. When polled, SRQ indi-
cates a service request has occurred. When read, SRQ indicates that an enabled status bit is set.