The Tau2 EXT_SYNC definition specifies 100ns sync pulses. Do the pulses have to be that short for a Tau2 to sync as a slave?
In external sync slave mode, the Tau2 triggers on the leading (low-to-high) edge of a sync pulse that is at least 100ns long. In master mode, the Tau2 will output 100ns EXT_SYNC pulses.