Designers should ensure that the SRST signal is de-asserted before the POR signal is de-asserted when laying out Zynq-7000 boards. This issue is related to (Xilinx Answer 52013).
Frequently Asked Questions About This Recommendation
Q1. Does this recommendation only affect initial power on?
A1. No, this also applies to reset sequences when the system is already up and running.
Q2. Can PS_SRST_B be pulled High if it is not used?
A2. Yes. Pulling PS_SRST_B High is the de-asserted state, so this would mean that it does not conflict with PS_POR_B.
Q3. Does this mean that PS_SRST_B cannot be asserted when PS_POR_B is asserted?
A3. No, PS_SRST_B can be asserted at the same time as PS_POR_B but PS_POR_B must be the last signal that is asserted.
Q4. How does this recommendation affect the release order of PS_SRST_B and PS_POR_B?
A4. PS_POR_B should be the last signal de-asserted and PS_SRST_B should not re-assert until after the BootROM is complete.
Q5. Does PS_SRST_B have to connect to an external sequencer/supervisor device?
A5. No, there is not a requirement to use a sequencer/supervisor, but it makes design easier and more straightforward. Managing this sequence can be done manually as long as the designer is careful to follow the recommendations above.