USB-6509 Theory of Operation

The USB-6509 features 96 TTL/CMOS-compatible digital I/O lines, a watchdog timer, digital input filtering and change detection, output programmable power-up states, and an optional external DC power supply for increasing the I/O drive strength.

You can configure I/O direction as input or output on a per-port basis. All samples of static DI lines and updates of DO lines are software-timed. Each I/O line has a 100 kΩ I/O pull resistor which you can select using the I/O line pull switch on the back panel.