Why this PBP code will blink PortB LED's but not the one on PortC?


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  1. #1
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    Default Re: Why this PBP code will blink PortB LED's but not the one on PortC?

    Quote Originally Posted by HenrikOlsson View Post
    Hi,
    The code targets the 18F4550 so I'm guessing that's it. PortC4-5 are the USB-pins which is probably why they can't be made into normal outputs - for some specific reason.

    /Henrik.
    Thanks, Dave and Henrik. Yes, I am using a 18F2550_4550, and I missed that in the Data sheet. Since my PCB is already designed for the 28 pin 18F2550, I guess my only recourse now is to find a 28 pin chip counterpart to the 18F2550 that doesn't have USB that will let me use the RC4 and RC5 pins as outputs. Thanks so much for setting me straight on this....I have been troubleshooting this for 5 days and never thought to check out the multiplexing of the RC4/RC5 pins.

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    Default Re: How to replace 18F2550 with function/pin equivalent that still provides I2C?

    OK guys...one more question that I hope you will help me answer. I have been looking for a replacement MCU that has all the functions of the 18F2550 that I have been using except the USB module, and that is pin compatible to the 28 pin version of the 18F2550. The closest I have so far been able to find is the 16F886, which appears to be pin compatible and has all the functions. However, one difference I can't quite resolve:
    1) The 18F2550 in my application is wired on my PCB to use its SDA pin 21 and its SCL pin 22 in an I2C interface to control two peripheral devices.
    2) Since I am looking to replace the 18F2550 on an existing PCB that is already routed that way, I need to confirm I can still use the 16F886 pins 21/22 as SDA/SCL signals to control the I2C devices.
    3) The data sheet on the 16F886 says it supports I2C interface, but requires use of RC3(pin15)/RC4(pin16) as SCL and SCD respectively, which pins I already have routed on my PCB for other functions.

    Somewhere I seem to remember someone on this forum saying that the SCL and SCD pins on MCUs only have to be used in an I2C interface when the MCU is operating as a slave and if it is the Master controller for other devices operating as slaves, that any I/O pins can be used as the outputs for the I2C control bus. Is that true? If so, how do I set up other PortB pins 21/22 as the I2C bus interface to control my peripherals?? Would really appreciate your advice on this!
    Last edited by jellis00; - 24th September 2011 at 00:15.

  3. #3
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    Default Re: How to replace 18F2550 with function/pin equivalent that still provides I2C?

    If you can re-do your code to use the I2CREAD/I2CWRITE command then you should be good.
    Dave
    Always wear safety glasses while programming.

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    Default Re: Why this PBP code will blink PortB LED's but not the one on PortC?

    Hi,
    To expand on Dave's answer a bit... If you're using the I2C peripheral (MSSP module) in the PIC then you must use the pins to which this peripheral is connected (on some PICs you can switch them to alternative pins but I don't think that's possible on the 16F886). If you're using I2CWRITE/I2CREAD, which is bit-banged and doesn't use the MSSP module, you can use "any" pins you want - as long as the pin used for clock can be an output and the pin used for data both in (for I2CREAD) and out (for I2CWRITE).

    It's true that the MSSP module (the SCL/SDA pins) HAVE to be used when the PIC is the slave but it CAN equally well be used when the PIC is the master. However, there are no PBP commands to directly "drive" the use of the MSSP module (like there is for the USART etc).

    /Henrik.

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    Default Re: Why this PBP code will blink PortB LED's but not the one on PortC?

    Really? I never thought about pbp doesn't support slave mode for I2C. This certiainly makes me re think so mtuff I am currently working on. Hmmmm shame.
    -Bert

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    http://foamcasualty.com/ - Warbird R/C scratch building with foam!

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    Default Re: Why this PBP code will blink PortB LED's but not the one on PortC?

    When using I2CREAD/WRITE the PIC is "in control" of the line, ie it supplies the clock and is therfor the master (same as with SHIFTIN/OUT). Because of this IC2READ/WRITE won't work for a slave type device, however the MSSP module setup in I2C mode will, you just have to "drive it manually".

    /Henrik.

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    Default Re: Why this PBP code will blink PortB LED's but not the one on PortC?

    Thanks henrik, just in time to fix what I was doing. I think I did some bit banging slave stuff a few (>5) years ago in ASM, no desire to repeat that!! Off to make sure chip selection supports slave mode I2C.
    -Bert

    The glass is not half full or half empty, Its twice as big as needed for the job!

    http://foamcasualty.com/ - Warbird R/C scratch building with foam!

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