Limit-Test Pass/Fail Ttl Input/Output - HP 8712ET User Manual Supplement

CAUTION

Limit-Test Pass/Fail TTL Input/Output

When limit testing is turned on, the LIMIT TEST IN/OUT rear-panel
BNC connector indicates the status of the limit test. If the limit test
passes, this TTL output goes high. If the limit test fails, this TTL output
goes low. This signal can be used, for example, as an input to a materials
handler.
Since the TTL output has limited current drive capability, it should be
buffered when controlling high current devices such as mechanical
relays. Otherwise, damage to the instrument may result.
The limit-test TTL can also be used as a general-purpose input, since the
analyzer drive to this line is open collector. When used as an input, limit
testing should be turned off so the instrument will allow the limit test
line to float high. The line can then be connected to an external switch
which should only pull the signal to ground or let it float (an external
circuit should not drive this line). A push button or foot switch can be
attached to the line to pull the signal to ground.
The state of the signal can be monitored by the automated system to
determine when the operator is ready for some action. The state of the
limit TTL line can be read with either the SCPI commands
20 INTEGER X
30 OUTPUT 716;"DIAG:PORT:READ? 15,2"
40 ENTER 716;X
or using the IBASIC command
30 X=READIO(15,2)
Finally, the LIMIT TEST TTL IN/OUT line can be used as a
general-purpose output line. With limit testing turned off, the state of
the line can be set to logic high or low with either the SCPI command
"DIAG:PORT:WRITE "
or with the IBASIC command
"WRITEIO ,value".
The following is an example of reading the LIMIT TEST TTL IN/OUT
line when used as an input:
30 Limit = READIO(15,2)
40 ! The "Limit" variable will be set to 0 if the signal is low
50 ! and 1 if the signal is high.
Automating Measurements
Operator Interaction
Limit-Test Pass/Fail TTL Input/Output
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