3-39
3
3.8.3.2 Using SRQs to Input Data
The 4863 can be set to monitor the status inputs, digital lines or the EDR
flip-flop and generate an SRQ (2363 generates a SRM) when selected input
signals change state. The signal changes are collected in the individual
event registers and summarized in the Status Byte Register. Refer to the
488.2 Status Structure in Figure 3-2.
When the SRQ is sensed, the user queries the Status Byte and then the
appropriate event register to determine the cause of the SRQ. The following
example generates an SRQ whenever the EDR flip-flop becomes set
(external data is ready) or the Status A signal goes low (In the example of
2.10, the external device has lost power).
Setup:
STAT:OPER:PTR 4
'enables bit 2 to set on EDR
STAT:OPER:NTR 1
'enables bit 0 to set on a nega-
tive transition of Status A
STAT:OPER:ENAB 5
'enables Event bits 0 and 2
*SRE 128
'Status Byte bit 7 enabled
After the SRQ occurs:
Serial Poll the 4863
If Status Byte bit 5 is on then
Read the ESR Register
If ESR bit 6 then
Read the input data
Else
Report error!!!
End If
Else If Status Byte bit 7 is on then
Print "External Unit off line" + (TIME)
Beep
Else
Report error!!!
End If
