The Series 2 LNL-1320 can use 12 or 24 volt DC input power. This was a change from the Series 1 LNL-1320 boards.
To accommodate the new voltage selection on the DC input power, there is a jumper for 12 VDC input or Pass-through (PT) to select the voltage level output to the reader.
The 12 VDC select jumper is used when the LNL-1320 is powered from 24 VDC. This causes the LNL-1320 to voltage divide the output to the reader so that it is a constant 12 VDC. It effectively divides the voltage in half.
The Pass-through select jumper is used when the LNL-1320 is powered from 12 VDC (e.g. passes 12 VDC through to reader).