Yes, you can synchronize DI and DO on a single NI 9401 (or across multiple modules). To do this on a cDAQ-9172 chassis you need to have the module(s) in slots 1-4. You'll need to create two tasks, one for input and one for output. Make sure you follow the reservation steps I discussed earlier so you can do input and output on the same module. You will also need to configure timing. The goal is to clock in/out data at the specified time.
The digital engines on the cDAQ-9172 cannot generate their own sample clock like analog input and output can so you'll need another source for the clock. This is called correlated digital. It is pretty common to use a sample clock from an analog task for digital but if you don't want/need your digital data correlated to an analog task, you can use one of the onboard counters to generate your clock.
To do this, create a pulse train generation task (there are some examples for this). Set your counter to /cDAQx/_ctr0. On your digital tasks, set the sample clock source to /cDAQx/Ctr0InternalOutput. This will allow you to use the internal chassis counters.
There are examples for timed digital (such as Read Dig-Ext Clk and Write Dig-Ext Clk).
I can go into a bit more detail if you necessary.
