Digital input and output

Micro1401

The Power1401 has full 16-bit digital input and digital output available on rear-panel D-connectors marked Digital Inputs and Digital Outputs. Bits may be read or written singly, by low or high byte, or by the whole word. High-byte output bits 0 and 1 are also routed to the front-panel Digital Outputs, and, if enabled by software, high-byte inputs 0 and 1 are fed from the front-panel Event Inputs.

The input high byte can be programmed for detection and timing of change of state (i.e. any bit changing in either direction). Digital output can be gated with clock 2 so that it updates on clock 2 ticks. Digital output is normally permanently enabled, but either byte may be turned tristate-off by software. It can also be controlled by pin 11 of the output socket. If pin 11 is grounded, both bytes are disabled, i.e. tristate-off ; they are enabled if pin 11 is high or disconnected.

Digital I/O LEDs

Front-panel event-input LEDs flash on detection of active-edge transitions. The quiescent state is set by software command. Front-panel digital-output LEDs simply reflect the state of the bits, being lit whenever their bit is set (high).

Technical details

Front-panel digital I/O is routed through common-mode ferrite chokes to prevent radiation of EMI. Outputs are buffered through 74ACT374s, which can source or sink 24mA.

Unconnected digital inputs read 1, being pulled internally to +5V by 4k7 (rear panel) or 100k (front panel) . Input voltages of more than 2.0V will always read as a logic 1. To appear as logic 0, the input must be pulled down to below 0.8V for at least 1microSec, which takes approximately 1mA (rear), 50microA (front).