General Purpose Inputs
The I/O controller manages:
- 4 general purpose inputs
- 4 general purpose outputs
- 1 watchdog output
- 1 temperature monitor
Configuration
The inputs are initially configured at power-on as follows:
- 4 kW impedance threshold
- TTL voltage threshold
- 100 millisecond de-bounce filter off
The initial configuration is suitable for both TTL signaling and contact closure devices. Alternate threshold voltages can be selected, for each input style individually through the Virtual File System API.
Threshold |
Threshold voltage |
Notes |
TTL |
1.5 V |
For TTL signaling and contact closure devices. This is the default configuration. |
CMOS |
2.5 V |
For 5V CMOS signaling. |
12V |
6.0 V |
For 12V signaling. |
Alternate time constants can be selected, for each input filter individually, through the Virtual File System API.
InputFilter |
Time constant |
Notes |
Off |
|
Filter is turned off. |
10ms |
10 ms |
Filter is turned on with a 10ms time constant . |
100ms |
100 ms |
A 100ms filter is very efficient to reject 50/60Hz perturbation. This is the default configuration. |
Alternate impedance thresholds cannot be selected.
State
The I/O controller measures both the voltage and the impedance across every input at a rate of 200 Hz. It compares the measured values with the threshold and determines the input state according to the following resolution table:
Measured impedance |
Measured voltage |
State |
Below impedance threshold |
Below voltage threshold |
Low |
Below impedance threshold |
Above voltage threshold |
High |
Above impedance threshold |
Don't care |
Disconnected |
The input state is reported through the Virtual File System API. The value must be interpreted differently according to the type of device attached to the input:
Level |
Meaning for contact devices |
Meaning for logic devices |
Low |
Contact is closed. |
The logic level is 0. |
High |
N/A. |
The logic level is 1. |
Disconnected |
Contact is open. |
The line is disconnected. |