Analog & Digital Cable Tester
There are two general modes. The first, which needs no accompanying computer, checks continuity on each line and checks that there is no short with nearby conductors. Success is indicated by LEDs.
In the second mode, the unit has capability of measuring resistances on each line to determine the quality of the connector installation and the resistance between any line and the adjacent lines. A set of solid-state switches driven by CPLD circuits makes the connections necessary for the resistance measurement.