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Interrupts in MSP430

Ankur Tech
Intellectual 360 points
Other Parts Discussed in Thread: MSP430G2553

1.

Is it possible to directly tie up a in to VCC in MSP when I use pull down resistor for interrupt. Won't it allow more current to flow & damage the pin.

 

2. Is it possible to make int configured for both H-L & L-H.

  • 0
    Genius 4925 points

    The details depend on the device you are using but in general the internal pull-up/pull-down resistors are 20kOhm - 50kOhm, so the maximum current will be 0.18mA. This current is quite small and should be no problem at all except you plan on using hundreds of pins in that configuration.

    Do you want to have an interrupt on one port for both directions at the same time? That is not possible as far as I know. You can configure it to be either H-L or L-H using the PxIES register but not both.

  • 0 in reply to Bernhard Weller
    Intellectual 360 points

    I am using MSP430G2553, max current 6mA. Is it safe to connect directly VDD to any pin.

  • 0 in reply to Ankur Tech
    Genius 4925 points

    It's safe as long as you can guarantee that nowhere in your software you switch the pin to output direction and pull it to ground. Then you will have a short circuit and the current will kill your device.

    As it is always possible that something goes wrong, maybe due to EMI it's safer to put a current limiting resistor in front of the pin.

  • 0 in reply to Bernhard Weller
    Guru 227245 points

    Bernhard Weller said:
    It's safe as long as you can guarantee that nowhere in your software you switch the pin to output direction and pull it to ground. Then you will have a short circuit and the current will kill your device.


    Not necessarily. The MSP can stand quite large amounts of abuse :)

    Actually, the por tpin driver will drive as much current it can until the voltage drop is too large for more current.

    The port pins can drive much more than 6mA. 6mA is the limit for maintaining the specified high/low output values. On 30mA or so, the drop will go up to VCC, the transistor is saturated. This will, however, be a heating power of 3V*30mA = 100mW. On a single pin, the MSP might stand this for minutes and you'll feel it going hot. Of course sooner or later it will burn-out the pin transistor.

    The original concenr might have been about the maximum input current to input pin.
    This refes to the clamp current that flows from any voltage above VCC or below VSS to VCC/VSS through protection diodes. These diodes will melt if a rated current above 2mA flows through them, either ceasing operation or shortcutting the pin to VCC/VSS.
    However, normal operational current (output current, or pulldown current) is independent of this limit.

    But you're right, a protection resistor is a good idea. Especially if it may happen that the port pin is sourced while the MSP is not. Because then VCC is 0V and input is 3V which is 3V too much. Then a limiting resistor would be a very good thing. We usually have 1k resistors in series to our inputs. Doesn't hurt but may save our a** :)

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