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/RST optional for Jtag? MSP430x2xx Family

Other Parts Discussed in Thread: MSP430F235

Hi,

I´m using the MSP430F235 in my design. My question, is the /RST Pin nessesary for the jtag or optional?

If optional i will pullup the pin to 3,3V with a 47kOhm resistor.

Thanks in advance!

  • Chris Zagel said:
    My question, is the /RST Pin nessesary for the jtag or optional?

    For 4-pin JTAG, the pin is optional. It is, however, commonly used to bring the MSP into a defined state before doing things like flashing. The pullup won't hurt in this case (and you should also add a pulldown capacitor of 10 to 100 nF).

    If you use SBW (serial JTAG) protocol, then /RST is required as clock pin. Resistor and capacitor still are recommended, but the capacitance should be 2.2nF max, or resistor/capacitor should be separated from the RST pin by a series resistor of >1k, so it won't act as low-pass to the SBW clock signal.

  • Thanks for your answer. I realised a 4-wire Jtag for the MSP430f235.

    I connected the pins TDO,TDI,TMS,TCK and VCCTarget,GND to the JTAG interface MSP-FET430uif.

    The /RST pin is fix pullup to 3,3V and connected to a pulldown capacitor.

    If I want to debug the microcontroller with CCS 5, the target is unknown and I cant programm the chip!

    What should I do?

  • Chris Zagel said:
    I connected the pins TDO,TDI,TMS,TCK and VCCTarget,GND to the JTAG interface MSP-FET430uif.

    For 4-wire JTAG you also need to connect:

    a) The TEST pin, since it is used to enable the JTAG signals.

    b) The  RST pin to interface with MSP430 development tools and device programmers.

    For further details on interfacing to development tools and device programmers, see the MSP430 Hardware Tools User's Guide, literature number SLAU278. 

  • Chester Gillon said:
    a) The TEST pin, since it is used to enable the JTAG signals.

    There are MSPs which have dedicated JTAG pins and not TEST pin at all. But right, if it exists, it eithe rneeds to be connected to the FET or tied to VCC for permanently selecting the JTAG use for the pins. (this may slighly increase power consumption)

    About RST, it is no base requirement to be connected to the FET. The FET may also reset the chip by switching VCC off (in case the MSP is powered by the FET). Also, JTAG can take over the MSP without resetting it first. But if the tool assumes that the MSP is freshly reset, well, then it might indeed be necessary. Not for JTAG itself, but for the tools used.

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