The new PSXX can detect when a block is occupied via current or photocell.

  • J4-5 [-] and J4-6 [+] are open if the block is not occupied and are connected together [up to 5 mA] if the block is occupied. This is an optically isolated open collector transistor and provides no power.

CV50 Block Occupied Detection Method
● Default = 0.
● CV50=0 - Block Current controls Block Occupied output.
● CV50=1 - Photocell controls Block Occupied output.
● Block current is used to indicate the block is occupied and the train is somewhere within the block.
● Photo cell is used to indicate the train is at a specific point in the block

CV53 Enable Block Current Auto-Calibration
● Default = 0, no calibration.
● CV53=66 enables Block Current Auto-Calibration the next time the PSXX is turned on.
● CV53 is set to 66, power is removed, and JP1 is returned to the 2-3 position.
● When the PSXX is next turned on, it will measure the average Block Current and store the value in CV56.
● This will prevent the Block Occupied output from turning on due to any background current (such as from lights, switch motors, etc.) in the block
● The Block Occupied will turn on if the current in the block increases above the background value due to block occupancy
● The PSXX automatically returns the value to 0 after the block is calibrated.


CV54 Block Current Off Hysteresis sets the current level at which the PSXX turns on the Block Occupied output. This allows you to set a level above the leakage current on the track to prevent false indications.
● Default = 5
● The Block Occupied output will be OFF if the detected current is less than the sum of CV56 and CV54.
● In general, this value should only be adjusted if the Block Occupied output will not turn off and you have done an Auto Calibration (see CV53).

CV55 Block Current Trip Hysteresis
● Default = 4.
● The Block Occupied output will turn ON when the detected current is more than the sum of CV54, CV55 and CV56.
● In general, this value should not be adjusted unless the Block Occupied output is chattering on and off.


CV56 Average Unoccupied Block Current
● Default = 27, acceptable values 1 - 255.
● The average value of the current in the block that is just below the trip level.
● The value may be set manually as required
● Note: the current input uses a nonlinear function, so manual setting is by trial and error) or automatically using CV53.
● Any current above this value may cause the Block Occupied output to turn ON.
● When set automatically, a resistance of 3.3K will add enough current above the background to turn the Block Occupied output on.
● Increasing the value will increase the current required in the block to turn the Block Occupied output on.