Bus Triggering
’X’ will always cause the counter to start a new measure-
ment. X will work as group execute trigger, GET. ’X’ must
always be placed in the end of a program message.
Service Request
The counter can send a service request, SRQ, when it
wants service from the controller. After an SRQ, the con-
troller must execute a serial poll which means that it
must ask each of the instruments for status information
until it finds the SRQ-giving instrument, evaluate the
Status-byte of the instrument and then make a decision
what to do.
To enable the counter to send service requests, you
must set an SRQ-mask telling the instrument which con-
ditions will cause SRQ.
Command
Comment
MSR <number>
<number> is a decimal value
depending on selected SRQ reasons.
Bit
Decimal value
Reason for SRQ
7
128
Not used.
6
64
Time-Out.
5
32
Hardware fault.
4
16
Programming error.
3
8
Measuring stop enable.
2
4
Measuring start enable.
1
2
Ready for triggering.
0
1
Measuring result ready
*
.
*
If SRQ for Measuring result ready is selected, the
counter will stop and wait until the controller fetches the
result before a new measurement can start.
Write down the binary word for the required SRQ, then
convert it to a decimal value and insert the value as
<number>.
EXAMPLE: If you want SRQ to be sent when the time-
out elapses, when the counter is ready for triggering and
when the result is ready, the binary word required is
01000011 which is decimal 67; see table below.
Bit Value if
Example
the bit is 1
Binary
word
Decimal
value
7
128
0
0
6
64
1
64
Time-Out
5
32
0
0
4
16
0
0
3
8
0
0
2
4
0
0
1
2
1
2
Ready to trigger
0
1
1
1
Meas. result ready
+
67
Send MSR 67 to the counter.
Status Byte
The counter sends its status byte to the controller on a
serial poll. The bits in the status byte reflects different
events or conditions in the counter. There are two types
of status bits:
A conditional bit indicates the current condition of what
its monitoring, all the time.
An event bit indicate that an event has occurred. When
the event occurs, the bit is set to 1. It is not reset to 0 un-
til a new measurement starts.
The different bits indicate the following information:
Bit Function
7
Always 0
6
1 = SRQ has been sent
*
, otherwise 0 (Event bit).
5
Abnormal bit. Always 0 during normal
measurements,1 if something is wrong. Affects bit
0-3, see below (Event bits.)
4
0 = Main Gate closed, 1 = Main Gate open
**
3-0
Depends on Abnormal bit, see below (Event bits.)
Bit
Abnormal bit = 1
Abnormal bit = 0
3
Not Used
Measuring stop enable.
2
Time-Out
Measuring start enable.
1
Hardware fault
Ready for triggering
0
Programing error
Measuring result ready.
*
Only if SRQ-mask is set for Service-Request.
**
This is a conditional bit that monitors the Main-
Gate in the counter. When TOT MAN is selected
the bit will always be 0.
Measuring start enable indicates that the counter logic
is ready to start a measurement.
Measuring stop enable indicates that the counter logic
ir ready to stop a measurement.
These bits can be used to detect if the input signal to the
counter is present; If the counter never stops it’s meas-
urement and the status byte stops at:
XX00X1XX
No input signal. The measurement is ready
to start (bit 2 = 1) but the Main Gate has
not opened (bit 4 = 0).
XX011XXX
Input signal lost during measurement. The
measurement is ready to stop (bit 3 = 1)
but the main gate is still open (bit 4 = 1)
(X = don’t care)
NOTE: SRQ is normally not used for these bits.
Ready for triggering indicates that all preparations for
a measurement is completed. The preparation time de-
pends on selected functions. It can be up to 700 ms
(when auto triggering is selected).
If triggered mode is selected, the counter waits to be trig-
gered, otherwise it proceeds with the measurement. You
can have the SRQ-mask set for SRQ at ready for trigger-
Page: 26
GPIB-INTERFACE OPERATION
PM 6669 - OPERATORS MANUAL