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SRQ Force Service Request
Interface Differences
As implemented on the HP-IB interface, an spectrum analyzer service request asserts the SRQ
control line on the HP-IB.
On the RS-232 interface, the spectrum analyzer does not have a way of signaling the interrupt
condition to a controller. In this case, the controller must operate in a polled mode if it requires
interrupt information (see “Polled Mode of Operation” below for a discussion of the polled
mode).
Interrupt-Related Commands Common to All Interfaces:
n
CLS Clear status byte, without read.
n
RQS Request mask.
n
SRQ Force service request.
n STB Read then clear status byte.
The HP-IB interface supports interface commands to read the status byte.
On HP-IB in HP 9000 Series 200 or 300 BASIC, the statement SPOLL (Device-address) can be
used to read the status byte.
Polled Mode of Operation
The polled mode of operation is probably most applicable to an RS-232 interface user. Because
there is no interrupt signal to the RS-232 controller, the user must periodically ask the spectrum
analyzer, via the “STB?” command, for the contents of its status register. For example, the
RS-232 controller could periodically check for the hardware-broken condition by executing the
“STB?” command and reading the results.
Status Byte Definition
The status byte sent by the spectrum analyzer determines the nature of the service request.
The meaning of each bit of the status byte is explained in
Table
B-l.
I
Bit
Message
0
(LSB)
Unused
1
Unit Key Pressed
2
End of sweep
3
Hardware broken
4
Command complete
5
Illegal spectrum analyzer command
6
Universal HP-IB service request HP-IB
R&S
bit
7
Unused
‘Ihble
5-10. Status Byte Definition
Display Message
SRQ 102
SRQ 104
SRQ 110
SRQ 120
SRQ 140
The display message is an octal number based on the binary value of the status byte. This
octal number always begins with a
u
1” since this is translated from bit 6, the universal service
request bit. The status byte for an illegal spectrum analyzer command (SRQ 140) is as follows:
bit number 7 6
543
210
status byte 0 1
100
0 0 0
5-522
Programming Commands