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RM48L530: RM48L530

Part Number: RM48L530

Dear sir / madam,

I would be very grateful if you could check the circuit attached regarding the Oscillator and JTAG interface.

The 2 things I am unsure of are:

    1. The oscillator we are using is an oscillator module (i.e. for better reliability) which has a single output which I have connected to OSCIN. Thus OSCOUT and KELVIN-GND are unconnected.
    2. We are using a 5V oscillator output which step down to 3.3V level using a potential divider (this has worked ok before on a PIC 3V3 micro)/
    1. The reset from the JTAG device is connected to the warm reset (nRST) of the micro is that correct?
    2. On other micro's we have connected this to the reset pin as there is usually only one. In this case could it be connected to the power on reset (nPORRST)?

p.s. I have based the design on the RM48 HDK development board.

Many thanks

Brendan Johnson


  • Hello Brendan,

    I will forward your post to one of our HW experts so they can review your JTAG circuit. You may also want to do a search of this E2E as I know there have been many threads on this topic already so there may be some helpful information found in doing such a search.

    In regard to your oscillator circuit, I don't anticipate there would be an issue with it. This would be similar to attaching a frequency generator in the same way on a bench; correct? My only caution is to be careful in the hookup of ground so that you don't get ground noise propagated into the device.

    In regard to hooking up nRST vs. nPORRST, I would recommend you stay with the nRST pin. A power on reset will cause all debug context to be lost when debugging if you assert reset during debug and connected to the nPORRST pin. nRST is a soft reset which means information is retained through the reset including debug context as well as potential sources of errors/exceptions that can be helpful in debug.
  • Many thanks Chuck.

    Regarding the oscillator, it will be a permanent oscillator module on the PCB rather than a standard oscillator and external components.
    Oscillator modules are more accurate and less hassle than an oscillator with external components.
    Which GROUND are you referring to? I guess you were thinking I was hooking up a frequency generator, but I won't be.

    I will await feedback from you hardware engineer.


  • Hello Brendan,

    1. I recommend to add an external pull-down resistor on nTRST
    2. Use pull-down for TCK instead of pull-up
  • Brilliant,


  • Hi Bendan,

    I was expecting that it was an independent clock generation circuit similar to a frequency generator but not one specifically, The device is fully capable of operating with an external clock source applied to OSCIN as you have indicated so this shouldn't be an issue. My comment with respect to the GND of this circuit was to make sure that the OSCILLATOR circuit doesn't create GND noise which is the purpose behind the Kelvin GND as a separate GND on the device. This is assuming that the circuit will have to be tied to the same GND as the MCU so it has the same GND reference.