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FM-55 / Aug 2014
G E N E R A L I N F O R M A T I O N
General Purpose Interface (GPIO)
The AM-55 is equipped with two General Purpose input (GPI) and output (GPO) ports
on the rear RJ-45 connector. The General Purpose connections are optically-isolated from
AM-55’s internal circuitry to prevent external ground loops and to prevent dangerous
voltages from being introduced into AM-55.
• GP Input #1 – Forces Analog Input regardless of currently selected input.
• GP Input #2 – Forces Digital Input regardless of currently selected input.
• GP Output #1 – Analog Input is selected.
• GP Output #2 – Digital Input is selected.
Each of the General Purpose inputs is current limited by 475 Ohm internal resistance.
The LED device inside the opto-isolators is rated at a maximum forward current of 50mA
and a normal operating current of 5mA.
APPLIED VOLTAGE TO GPI
EXTERNAL RESISTANCE
3.3 Volts
None
5.0 Volts
330 Ohms
6.0 Volts
470 Ohms
7.5 Volts
820 Ohms
10.0 Volts
1.3 kOhms
12.0 Volts
1.8 kOhms
12.0 Volts
2.4 kOhms
24.0 Volts
3.9 kOhms
30.0 Volts
5.1 kOhms
*48.0 Volts*
9.1 kOhms
Before connecting external circuitry to the General Interface inputs,
first ascertain whether it will be necessary to utilize additional outboard
series resistance in your application!
Use the following table to determine if an external resistance is required and if so, what
value it should be. Note that a one-half watt resistor is sufficient. The resistance values in
the table below have been calculated to result in approximately 5.0 milliamperes forward
current through the opto-isolator’s internal LED.
* For personal safety reasons a voltage in excess of 48VDC is
NOT recommended to be applied to the General Purpose inputs.
The opto-isolators on the General Purpose outputs protect internal AM-55 circuitry
from voltage up to 350 volts AC or DC. The MAXIMUM permissible load current is
100 milliamperes (0.10 Amperes).
