Devices that emulate the 8255 protocol support two handshaking signals:
For input tasks, when the Handshake Trigger signal is low, the samples are sent to the measurement device. After the samples have been sent, Handshake Event is high, which tells the peripheral device that the data has been read. For digital output, Handshake Event is low while the NI-DAQmx device sends the samples to a peripheral device. After the peripheral device receives the samples, it sends a low pulse back on the Handshake Trigger line. Refer to your device documentation to determine which digital ports you can configure for handshaking signals.
The default terminals used for handshaking signals vary from device to device.