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MSP430BT5190 reset circuit

Nigel Wade1
Prodigy 110 points
Other Parts Discussed in Thread: MSP430BT5190

I would like to know what are the external component requirements of the reset circuit on a MSP430BT5190 micro controller. From what I have read, there seems to be some confusion.

I intend to run the micro off a CR coin cell battery (2.0 to 3.2V), with standard 6 wire programming, and (if possible) would like to use components that are already used on the board (10k, 100k, 100nF, 1uF). The standard values seem to be a 47k pull up, with a 2.2 nF pull down, however 10k pull up and 100 nF pull down is also mentioned. Then, some threads refer to later series MSP models having resistors or capacitors inside the chip.

Does the MSP430BT5190 have any pull ups / downs within the chip, and what range of components would work for my circuit?

  • 0 in reply to Leo Hendrawan
    Prodigy 110 points

    Thanks Leo.

    Referring to the user's guide for the 5xx series of MSPs, section 1.7 says an internal pull-up resistor is enabled, and that no external resistor is required. This would seem consistent with my development board still operating (and the RST pin sitting at Vcc), when I removed the external pull-up.

    Could you please confirm that this is the case, and for reliable operation, no external resistor is necessary.

  • 0
    Guru 227245 points

    Nigel Wade1 said:
    reset circuit on a MSP430BT5190

    IIRC, teh BT5190 is basically 1 5438 (non-A). On the non-A 5438, teh pullup on RST pin is there but not active by default. (so pretty much useless). On the A version (and AFAIK all other 5x/6x family devices), it is active on power-up.

    However, the internal pullup is rather weak. If you encounte rproblems with crosstalk causing a reset, you should use an external one.

    The 2.2nF cap is for the case you're using SBW protocol (which clocks the RST pin for the JTAG transfer). If SBW is not used, a bigger cap is better. The 10k/100nF combo provides a good timing and distortion-safety for a clean startup erven und bad conditions (EMI, crosstalk, slowly rising supply voltage etc.).

  • 0 in reply to Jens-Michael Gross
    Prodigy 110 points

    Thanks Jens-Michael

    After comparing the datasheets (specifically things like the max frequency, PMM and power consumption), to me it looks like the BT5190 is based on the 5438A device. Could you please confirm this?

    Even if the internal pull-up is enabled, for peace of mind, I will probably have an external one anyway. If I was going to use SBW programming, do you think a 10k / 2.2nF combination on the RST line would be OK?

  • 0 in reply to Nigel Wade1
    Guru 227245 points

    Nigel Wade1 said:
    After comparing the datasheets (specifically things like the max frequency, PMM and power consumption), to me it looks like the BT5190 is based on the 5438A device. Could you please confirm this?

    Hmmm, I said 'IIRC' and apparently I didn't. You're right, from the maximum frequency etc it rather looks like a 5438A.

    Nigel Wade1 said:
    Even if the internal pull-up is enabled, for peace of mind, I will probably have an external one anyway.

    The internal one, while sufficient to keep RET high, is pretty weak. Yes, an external one is a good idea if you actually connect something that could catch crosstalk 8especially if there is a JTAg connector but no JTAG atached that pulls the line high by itself).

    Nigel Wade1 said:
    If I was going to use SBW programming, do you think a 10k / 2.2nF combination on the RST line would be OK?

    The required R/C time depends on your power supply. The slower the voltage rises at power-on, the larger the time constant has to be for a proper startup.
    Even with SBW you can use a higher cap, but then you should separate the R/C combo from tthe RST pin and the SBW signal by a series resistor of 1 or 2k. This way, the capacitor won't affect the SBW signal much while still doing its job at startup.

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