ADLINK PCI-8164 - Manual (Page 295)

Connection Example 283
7.5.1 Wiring Example:
PEL, MEL, ORG, SD, PSD, MSD, and Alarm Clear (at IOIF):
CMP, LTC (at IOIF)
Z
CMP is a TTL 5V or 0V output (vs. Ext GND)
Z LTC is a TTL 5V or 0V input (vs. Ext. GND)