GTS Transceiver PHY User Guide: Agilex™ 5 FPGAs and SoCs
3.7.5. Input Reference Clock Buffer Protection
The GTS transceiver’s input reference clock buffers have a protection mechanism that prevents aging and damage to the buffers if the reference clock is left unconnected or there is no clock toggling activity on it. The protection mechanism detects when there is no toggling clock on the input buffers, and automatically turns off the buffers. The detection mechanism measures for clock frequencies from 25MHz to 380MHz, and any frequency outside this range causes the buffer to be turned off.
If the input reference clock is brought back up and stable, and there is a need to use it again, the buffer needs to be turned back on. There are two ways to do this:
- Reconfigure the device, or
- Request the device to re-enable the buffer. This can be done by using the register read/write method, or by using the optional status and control ports.
Refer to Buffer Turn-on Request via Register Method for the register read/write method of re-enabling buffers, or Buffer Turn-on Request via Status and Control Ports Method for the status and control ports method.
Below is the sequence of re-enabling the refclk buffer from the time the reference clock source is disabled or disconnected.