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124 Digital Port Functions
In Figure D-2, the INH input is connected to a switch that shorts pin 3 to pin 4 whenever it is necessary to externally disable
the output of the supply. This will activate the remote inhibit (RI) fault protection circuit, causing the front panel
Prot
annunciator to come on. It also sets the RI event bit in the supply's Questionable Status Event register (see "Chapter 4 -
Status Reporting" in the Programming Guide). To re-enable the supply after it has been disabled by the INH input, first
open the connection between pins 3 and 4. Then clear the protection circuit either from the front panel (see "Chapter 5 -
Front Panel Operation" in this guide) or over the GPIB (see the Programming Guide).
GPIB
Figure D-2. Example of Inhibit Input
In Figure D-3A, the FLT output is connected to a relay driver circuit that energizes a relay whenever a fault condition
occurs in the power supply. The relay can be used to physically disconnect the output of the power supply from the load.
The FLT output is generated by the logical ORing of the power supply's Operation, Questionable, and Event status summary
bits (see "Chapter 4 - Status Reporting” in the Programming Guide). You can cause one or more events to activate the FLT
output by enabling the appropriate events in these status registers. The fault condition is cleared by first removing the cause
of the fault and then reading the appropriate status event register(s).
In Figure D-3B, the FLT output of one supply is connected to the INH input of another supply. Although only two supplies
are shown, it is possible to chain other supplies with this arrangement. A fault condition in any one of the power supplies
will disable all of them without intervention either by the controller or external circuitry. The controller can be made aware
of the fault via a service request (SRQ) generated by the Questionable Status summary bit (see "Chapter 4 - Status
Reporting" in the Programming Guide).
Note The INH input cannot be used to disable outputs set from the external voltage programming port.