Voltage levels on JTAG pins

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shrutib

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Hello,

I am using 10pin JTAG header and have follwing voltage levels on pins when device is powered on:
TMS = 3.3V
TCK = 3.3V
TDO = ~2mV
TDI = ~2mV
nRESET = 3.3V

The problem is the controller is not responding when connected to debugger. should the voltage levels at TDO and TDI be also 3.3V? Is this creating problem or there might be some other reason?
Thankyou in advance.
 

As far as my experience, all the JTAG pins are held at logic 1 unless another JTAG device isn't connected to the port.
 

Pull-ups are specified by the JTAG standard for TDI, TMS and TRST "undriven input produces a logical response identical to the application of a logic 1".
TDO should be high Z as long as the TAP controller is inactive.

In so far, measuring low level at TDI indicates a problem, possibly a PCB short or damaged device.
 

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