MS9400 HD FrEND User Guide Chapter 7: Using the GPIO Control Interface
47 Rev. 1.50
Input Circuit Wiring Configuration
The opto-isolated input circuits provide for various connection scenarios, two common methods follow:
Option 1 – Input switch contacts using the GPIO’s own power supply. This method is useful in the majority of
applications when the current requirement is within the allowable limit of the MS9400 - 500mA available for
external use.
Option 2 – Input switch contacts using an external power supply. The voltage of the external supply is not critical
if the current through the internal 560ohm resistor is limited between 5 – 20mA. This method is preferred where
installation takes place in noisy environments, or where the switch contacts wiring is run over a long distance.
NOTE: It is imperative that the ground connection of the external PSU is connected to the ground terminal
on the FrEND.
Relay Changeover contacts (Digital Outputs)
GPIO output offers four (4) normally open/normally closed (NO/NC) sets of relay changeover contacts.
These relay outputs are used as switches to control external devices. Their activity is controlled by the GPIO
control sequence (macro) stored on the HD FrEND.
