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PicoZed Rev. E CARRIER_SRST# usage

mhn

On PicoZed Rev. E, the "Carrier RESET" is implemented like this:

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PS_SRST_B is connected directly to ZynQ-7000 PS_SRST_B_501.

The problem is that if I would like to use this signal from my carrier board e.g. by connecting a push button between CARRIER_SRST# and ground, the voltage level on PS_SRST_B may not be low enough to actually RESET the ZynQ chip.

If I connect CARRIER_SRST# to ground, the current flows through the Q6 diode, and the diode forward voltage is seen on PS_SRST_B. The Q6 datasheet doesn't give an explicit answer to this, because the current through 10K resistor is really low (the graph is drawn only to 1mA minimum, forward voltage is about 0.55V at 25 celsius). According to Xilinx ds187 the maximum low level limit for ZynQ-7000 PS_SRST_B_501 (LVCMOS18) is 35% of 1.8V i.e. ~ 0.63V.

Can you guarantee, that the Zynq chip is reset by pulling CARRIER_SRST# low over the entire specified operational temperature range, and in spite of component-to-component variance?

  • 0

    Hello mhn,

    I apologise if I am missing the question. Based on what you are saying you want to take the CARRIER_SRST# from the SOM and implement on your carrier card as push button when pressed down will send it to ground thus resetting the Zynq correct? And your worry is where it will actually be reset based on Xilinx ds187 correct?

    That is exactly what we do with the PicoZed FMC V2 Carrier Card we have as a reference.

    image

    We haven't seen any issues with resetting the device in this manner.

    You can find this schematic/supporting materials located here http://zedboard.org/support/documentation/13076

    Also, if you contact your local Avnet FAE, they can request the PicoZed FMC V2 Carrier Card Design files free of charge to assist with your carrier card development. The design files were generated using Altium.

    Thanks,

    Josh

  • 0

    Hi,

    Thanks a lot for your reply.

    If you haven't seen any issues with this method, then I guess its ok, but I wouldn't do it like that. I would pull the PS_SRST_B_501 pin closer to ground potential, not through a diode. But anyway, I'll need to measure this when I get my board.