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RM57L843: Board is not come out of Reset after XDS100V2 issue nTRST

Part Number: RM57L843

We are using RM57L843  for one of our control card. We are using XDS100V2. We found that when XDS100V2 is connected and trying to connect, it is generating nTRST high and then low and then high. It remain in high state. After that we found that RST pin and PORRST is going permanently unless XDS100V2 is disconnected or board is power cycle.

We are not able to understand the reason for this behavior.

Following is the pin state before nTRST:

RST- high

PORRST-high

nTRST-Low

After nTRST sequence:

RST- permanently low

PORRST- Permanently low

nTRST-High

Board remain in reset state.

Can you tell us reason for above behaviour.

  • Hi,

    Is nTRST connected to nRST and nPORRST? Is the power supervisor connected or driven by nTRST? nTRST is a tap reset signal, and should not be used to reset the device like nRST and nPORRST.

    Please double check your schematics and PCB board layout. 

  • nTRST is connected to nRST and not connected to nPORRST.

    nPORRST is connected with RC circuit with time constant of 10 msec.

    We have power supervisor to monitor 3.3 V, also one external watchdog timer with is generating RST from outside and connected to nRST of controller.

    I did not get the why nTRST can't be connected to nRST.

    Can you suggest how we can connect nTRST to nRST.

  • Sorry one correction in first line above, nTRST is not connected to nRST. nRST is driven by external watchdog timer. nTRST is only connected to nTRST pin of controller without any pullup or pulldown.

    We observed that when XDS100V2 is connected and debug started, nTRST finally went high and when nTRST is becoming high, nRST and nPORRST is becoming low and remain in that condition.

  • The nTRST has internal pull-down. It is fine without pull-down to nTRST.

    I don't know why the nRST and nPORRST are pulled down when nTRST is becoming high. As I said, please double check your PCB layout.