When configuring a device through Asynchronous Peripheral mode,
is the RDY/BSY pin still active when the DONE pin is held low
to stall startup and operation?
The RDY/BSY pin is active until the I/O's are released. With
the default makebits or bitgen options, the I/O's are released
after the DONE pin is released. So if the DONE pin is held low
(and SyncToDone is enabled, see comments below) then the
RDY/BSY pin will still be active.
However, the RDY/BSY pin will not indicate BSY (BSY = 0) just
because the DONE pin is being help low. The RDY/BSY pin will
only indicate BSY if the FPGA is serializing the data on the 8
bit data bus for configuration. If the DONE is held low, but
no data is being written to the bus, then RDY/BSY will indicate
The holding the DONE pin low can stall startup and operation
only if the SyncToDone option is enabled in makebits or bitgen.
If SyncToDone is not set then the FPGA will not monitor the
external state of the DONE pin, it will release the DONE pin at
the end of configuration and proceed with startup whether the
DONE pin is externally held low or not.