Interconnected chips and pin settings


Closed Thread
Results 1 to 5 of 5
  1. #1
    Join Date
    Dec 2008
    Posts
    16

    Default Interconnected chips and pin settings

    Noob playing with a 16f887 and a umFPU math coprocessor.

    After frying a couple of umFPUs I've realized that I need to be setting the TRISx and PORTx settings (see, noob). I think that after a number of power-on resets one of the Pic pins went high and nearly melted the breadboard under the umFPU and cooked the umFPU chip (but Pic was OK).

    I've now set the pins to inputs and set them low but am hesitant to potentially blow yet another chip. Is this the proper setting for pins connected to other chips? Is there any other option?

    Thanks.

    I think it was pin C4 or C5 that went high.


    '-------------------- uM-FPU pin definitions ----------------------------------
    FpuClk var PORTC.3 ' SPI SCLK (uM-FPU SCLK)
    FpuIn var PORTC.4 ' SPI MISO (uM-FPU SOUT)
    FpuOut var PORTC.5 ' SPI MOSI (uM-FPU SIN)

  2. #2
    Join Date
    Nov 2003
    Location
    Wellton, U.S.A.
    Posts
    5,924


    Did you find this post helpful? Yes | No

    Default

    What voltage are you running the PIC at and what is the max voltage of the other chip? The max voltage it can handle?
    Dave
    Always wear safety glasses while programming.

  3. #3
    Join Date
    Dec 2008
    Posts
    16


    Did you find this post helpful? Yes | No

    Default

    I am running both the 16f887 and umFPU at 3.3V.

    umFPU can run at up to 5V.

  4. #4


    Did you find this post helpful? Yes | No

    Default

    can you not put resisters between the pic and the mathco? that should stop the mathcpu from grounding sending a pic output line to ground and poping the chip...

    But yes, the startup of the chip needs to send all outputs low and then set the relivant lines to inputs right at the beginning...

    So...

    Code:
    TRISE = %00000111
    TRISD = %00000000
    TRISC = %00000000
    TRISB = %00000000
    TRISA = %11111111
    PORTA = 0
    PORTB = 0
    PORTC = 0
    PORTD = 0
    PORTE = 0
    Setting TRIS to 1 makes that bit an input...
    the PORT commands makes all the ports low...

    I hope that helps

  5. #5
    Join Date
    Dec 2008
    Posts
    16


    Did you find this post helpful? Yes | No

    Default

    Thanks Comwarrior, I think that resistors between the two processors is what was needed.

Similar Threads

  1. Help using 74LS165 & 74LS164 chips with my 16F84A
    By studysession in forum mel PIC BASIC Pro
    Replies: 0
    Last Post: - 2nd March 2009, 11:36
  2. pin 12f683
    By jcleaver in forum mel PIC BASIC Pro
    Replies: 22
    Last Post: - 22nd March 2007, 23:29
  3. Another RTC, DS1287
    By DavidK in forum Code Examples
    Replies: 0
    Last Post: - 12th December 2006, 18:07
  4. Multiple Data on to USART RX pin
    By Squibcakes in forum Serial
    Replies: 2
    Last Post: - 20th July 2006, 01:37
  5. I/O pin and MCLR
    By Dwayne in forum FAQ - Frequently Asked Questions
    Replies: 1
    Last Post: - 15th July 2004, 11:52

Members who have read this thread : 1

You do not have permission to view the list of names.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts