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MSP430F2012 RST/NMI capacitor and Resistor

Eric Eckenrode
Intellectual 275 points
Other Parts Discussed in Thread: MSP430F2012

Hello,

I have been looking closely at the MSP430F2012.  The application is very space constrained.  I see in the user's manual on page #41 that a pullup of 47Kohm is reccomended and a max of 2.2 nF cap is also recoomended. 

MSP430x2xx Family User's Guide

http://www.ti.com/lit/ug/slau144j/slau144j.pdf

 

I also see in the user's guide for the eZ430-F013 Development tool on pg 11. that the schematics do not show the resistor or the capacitor

eZ430-F2103 Development Tool User's Guide

http://www.ti.com/lit/ug/slau176d/slau176d.pdf

 

Do I need them or can I get away without using them?

 

Thanks,
Eric

  • 0
    Prodigy 210 points

    From slau114j.pdf (page 33): "2.2.1.1 Reset/NMI Pin
    At power-up, the RST/NMI pin is configured in the reset mode. The function of the RST/NMI pins is
    selected in the watchdog control register WDTCTL. If the RST/NMI pin is set to the reset function, the
    CPU is held in the reset state as long as the RST/NMI pin is held low. After the input changes to a high
    state, the CPU starts program execution at the word address stored in the reset vector, 0FFFEh, and the
    RSTIFG flag is set.
    If the RST/NMI pin is configured by user software to the NMI function, a signal edge selected by the
    WDTNMIES bit generates an NMI interrupt if the NMIIE bit is set. The RST/NMI flag NMIIFG is also set."

    If RST/NMI pin is configured in the reset mode, RC chain is required (without the program does not begin its work).


    Please see http://www.ti.com/sc/docs/products/micro/msp430/userguid/ag_03.pdf

    Page 4 - Global Interrupt Structure.

  • 0 in reply to Roman Kaban
    Guru 227245 points

    Roman Kaban said:
    If RST/NMI pin is configured in the reset mode, RC chain is required (without the program does not begin its work).

    Since at power-on the pin is in reset mode, the R/C is always required, or else the program that changes to NMI mode won't start.

    However, the purpose of the R/C is to keep the CPU in reset state while VCC is rising. it prevents the CPU to start up while VCC is still too low for proper operation. As long as VCC is still rising, the voltage on RST pin will be below VCC and hold the MSP in reset.

    The slower the supply voltage rises, the larger R and C have to be. If the reset pin is handled by a reset controller (or the FET), of course no R/C is required.
    Also, if the device is being programmed by SBW mode rather than 4-wire JTAG, C shouldn't be larger than 2.2nF.

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