See TL-X for newest architecture.
The Digital TTL/CMOS I/O module provides 16 individual channels which are programmable for either Input or Output, and include extensive diagnostics. Interrupts can be selected, for each channel, to indicate transition on rising edge, transition on falling edge, or both. De-bounce circuits for each channel offer a selectable time delay to eliminate false signals resulting from contact bounce commonly experienced with mechanical relays and switches. Each TTL/CMOS channel has an internal 110KO pull-down resistor. All inputs are continually scanned and the data is double buffered for immediate availability.