VISA write at constant clock

[engata]

I am using a PXI 6221 for analog inputs and a PXI 8344/4 to communicate 2 absolute encoders. I have a sample clock runs at 4kHz for my analog inputs. What I need is to send a command to encoders at the beginning of each sample clock cycle. That command is needed to receive the current encoder position which should be synchronized with my analog data. So, I am trying to synchronize the first falling edge of the TX pin with the sample clock; please see the attached pic. Should I use VISA event functions?

Thanks