Hello Mike,
in the USage guidelines says:
When the serial line protocol goes down (for example, because of loss of synchronization), the interface hardware is reset and the DTR signal is held inactive for at least the specified interval.
>>This function is useful for handling encrypting or other similar devices that use the toggling of the DTR signal to resynchronize.
This command create a pulse signal on the DTR pin that allows the attached device to detect a requesto to resync.
In the example for a 2Mbps serial interface there is 3 seconds.
Fo HSSI it has be in the order of 150ms
Hope to help
Giuseppe