Input Configuration

For GPI configuration, you have two signal modes available: Mode “Differential”, and mode "Single-ended". Mode "Differential" is the default mode.

In mode “Differential”, you can use the GPIs on the Front GPIO for receiving either up to 3 differential signals, or for receiving two differential signals and one single-ended signal.

In mode Single-ended”, you can use the GPIs on the Front GPIO for receiving up to 4 single-ended signals.

 

You can switch between the modes "Differential" and "Single-ended" using the command line tool as described in Configuring the Physical Properties of Trigger Signals.

Differential Mode (Default Mode)

In default configuration (“Differential” mode), all the six input pins of the Front GPIO are configured to receive differential signals (in pull-up mode):

 
  • Pins 8/9
-> 1 differential signal (pin 8 +, pin 9 - )
 
  • Pins 11/12
-> 1 differential signal (pin 11 +, pin 12 -)
 
  • Pins 13/14
-> 1 differential signal (pin 13 +, pin 14 - )
 
  • Pin 10
-> GPI voltage IN (4,5 - 28 V): The GPI voltage IN must be the same voltage as the signal source voltage.
 
  • Pin 15
-> GPI GND

Alternatively, you can (in default configuration) use pin pair 8/9 to receive one single-ended signal:

 
  • Pin 9
-> 1 single-ended signal: You connect the single-ended incoming signal to the physical pin 9; Pin 8 is not connected.
 
  • Pins 11/12
-> 1 differential signal (pin 11 +, pin 12 -)
 
  • Pins 13/14
-> 1 differential signal (pin 13 +, pin 14 - )
 
  • Pin 10
-> GPI voltage IN (4,5 - 28 V): The GPI voltage IN must be the same voltage as the signal source voltage.
 
  • Pin 15
-> GPI GND

Single-Ended Mode

If you need more than 1 single-ended input signal, you can switch the GPIs of your Front GPIO into "Single-ended" mode. In "Single-ended" mode, the six input pins of the Front GPIO are configured to receive 4 single-ended signals:

 
  • Pin 8
-> 1 single-ended signal
 
  • Pin 9
-> 1 single-ended signal
 
  • Pin 11
-> 1 single-ended signal (pin 12 not used)
 
  • Pin 13
-> 1 single-ended signal (pin 14 not used)
 
  • Pin 10
-> GPI voltage IN (4,5 - 28 V): The GPI voltage IN must be the same voltage as the signal source voltage.
 
  • Pin 15
-> GPI GND

How to switch between "Single-ended" and "Differential" mode, see Configuring the Physical Properties of Trigger Signals.

Custom Configuration “Pull-Down”

 

Both configurations (Differential and Single-ended) can be used in pull-up and pull-down mode. Default is the pull-up mode. If you want to use the inputs in pull-down mode, you can configure the pins accordingly, see Configuring the Physical Properties of Trigger Signals.

   

Schematic Circuit Diagram Front GPIO:

Electrical Characteristics of the Physical Inputs:

Electrical

Minimum

Typical

Maximum

Unit

Supply voltage 4.5   28 V
Input threshold   20% Supply Voltage   V
Differential input offset voltage   10   mV
Current at GPI pin   4   mA
Total current at GPI voltage IN     50 mA

Timing Characteristics of the Physical Inputs:

Timing

Minimum

Typical

Maximum

Unit

Propagation delay 40 60 80 ns
Min. pulse width   200   ns
Max. frequency   2.5   MHz

 

Board Protection

 

LightBridge 2 ACL has been designed with a varistor which opens at an input voltage of 30V (on the GPIOs) to let the onboard surge protector get active to protect the board. At a total supply voltage of 36V, the electronic chips would become defective.