There are a number of important considerations for serial daisy chains:
- Start-up sequencing (GTS)
GTS should be released before DONE or during the same cycle as DONE to ensure the device is operational when all DONE pins have been released.
- Connect all DONE pins
It is important to connect the DONE pins for all devices in a serial daisy chain. Failing to connect the DONE pins can cause configuration to fail. For debugging purposes, it is often helpful to have a way of disconnecting individual DONE pins from the common DONE signal, so that devices can be individually configured through the serial or JTAG interface.
- DONE pin rise time
After all DONE pins are released, the DONE pin should rise from logic 0 to logic 1 in one CCLK cycle. See Configuration Pin Definitions for DONE signal details. If additional time is required for the DONE signal to rise, the DonePipe option can be set for all devices in the serial daisy chain.