Measurement Computing's CIO-DIO24H is a high-drive TTL board with 24 digital I/O lines, and one 82C55 parallel-interface chip. The I/O is configured as two 8-line ports and two 4-line ports based on an 82C55 mode 0 emulation. Each port may be individually programmed as input or output.
All digital inputs are LSTTL. The output signals are buffered, high-output drive TTL. The digital output drivers are 74S244 chips that can sink 64 mA and source 15 mA. The input buffers are 74LS373 chips and have standard high input impedance of the 74LS series devices.
All I/O lines are set to input mode (high impedance) on power up and reset. If you are using the board to control items that must be OFF on reset, install pull-down resistors. The board is equipped with open locations where you can install SIP resistor networks for either pull-up or pull-down.
All signals pass through a 37-pin connector.
