MKS Instruments UK Ltd
Cirrus2 Hardware Manual – SP101017.100 June 2011
16
Interfacing Notes
The 120mA maximum load for the power supply outputs is shared between the Digital and Analogue connectors.
When interfacing digital signals between units the preferred method is to:-
a) Have a pull-up resistor/current source on all inputs to the local power supply rail. Often this feature is provided by the
digital input chip itself.
b) Use an open collector/drain/contact closure to ground as the output drive signal.
c) Where appropriate, arrange the hardware/software configuration so that an input Hi state is a safe condition. This
ensures that if a connection should be unplugged the system will go into a fail-safe state.
d) In cases where the external equipment is some distance away and/or is likely to have a different ground potential the
fitting of opto-couplers on the interfacing should be implemented.
Using this approach allows for easily interfacing between different voltage levels and logic families.