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msp430f4132: New to the forum, two quick questions

Robert Clark59
Intellectual 930 points
Part Number: MSP430F4132

Hi forum,

Two quick questions, processor MSP430F4132, 125 lcd segments driven, one SPI port used, one I2C port used (appear to not be conflicted),

1. Port pins P1.6 and P1.7 appear to be free of LCD drive and available for interrupt use. Only two interrupts are needed for this design, which is non-life threat and very low key. Are these interrupt lines actually available for use?


2. How long does it take in uS to start the interrupt program, release the interrupt line, increment one binary number, change it to bcd, and send it to the LCD register?


Thank you in advance, and have a great day!

Robert.

  • 0
    TI__Guru**** 212077 points
    Hi Robert,

    1. Yes, P1.6/P1.7 are interrupt-capable.
    2. This depends on the CPU frequency, LPM exited from, and number of cycles involved with performing the instructions (see Section 3.4.4 of the User's Guide), estimates can be generated but in the end it will be easiest to evaluate this case with a test setup.

    Regards,
    Ryan
  • 0 in reply to Ryan Brown1
    Intellectual 930 points

    Thank you for the quick reply.

    Let's assume 1Mhz to keep things low power, and only guessing within an order of magnitude. Also assume the only program running is looking for these two interrupts!

    Therefore, as above, service the interrupt, increment a register, convert to bcd, and write to LCD register. 10uS? 100uS? 500uS? 1000uS? 2000uS? 5000uS?

    I'm just trying to figure out if this design should stay discrete, or would it be better off with a processor. I'm a hardware guy, but have done a lot of programming. I just need someone with experience with these processors to get me in the ballpark.


    Thank you very much,

    Robert.

  • 0 in reply to Robert Clark59
    TI__Guru**** 212077 points
    It mainly depends on what's included with converting to bcd, that logic is probably what will take the most time. At 1 MHz each cycle is 1 us in length. Servicing the interrupts, increment a register, and writing to the LCD register will take about 20 us. The worst you are looking at is probably less than 50 us, but once again this is just a quick guess.

    Regards,
    Ryan

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