Circuit Description

The input/output devices in the PCM include analog-to-digital converters, signal buffers, counters, and special drivers. The PCM controls most components with electronic switches which complete a ground circuit when turned ON. These switches are arranged in groups of 4 and 7, called either a surface-mounted Quad Driver Module (QDM), which can independently control up to 4 output terminals, or QDMs which can independently control up to 7 outputs.