selection of resistor for protection on data and clock pins(PICkit2)

Discussion in 'Embedded Systems and Microcontrollers' started by sairfan1, Jul 3, 2012.

  1. sairfan1

    Thread Starter Member

    May 24, 2012
    46
    1
    hi,
    i'm using pickit2 for in-circuit debugging and programming for mcu 16F877A and some small MCUs like 16F88. as we use pin B7,B6 for debugging and in-circuit programming, we may use same pins for other purpose, for example
    LEDs (seven segments)
    LCD
    Some shift registers, ICs, sensors etc.
    how can i evaluate, value of resistor to protect these, and use these pins for multipurpose

    thanks.
     
  2. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    for LEDs you need at least 2.2K Ohm. IC input does not need protection (from RB6/RB7).
     
  3. sairfan1

    Thread Starter Member

    May 24, 2012
    46
    1
    470ohm already added, coz its separate module. still u think 2.2 is enough, and what about 16x4 lcd

    thanks in advanced
     
  4. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    have you inlined the 470 Ohm from the ICSP?

    That is not required. If you use LED, you must limit the current, or ICSP stops to work.

    For LCD you don't need any resistors, these are inputs.

    But avoid to drive RB6 RB7 with any signal going to the PIC.
     
  5. sairfan1

    Thread Starter Member

    May 24, 2012
    46
    1
    im sorry i did not well explained.

    B7 is connected with 7 segment's pin "g", and there is also 470Ohm resistor between B7 and "g", PICKit2's pin is directly connected with B7(there is not resistor in between PICKit2 and B7).
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    If you want to do debugging. The MCLR pin must be used as MCLR. And the pins connected to the PICKIT pin 4 and 5. Can not be used for anything else. It is only during ICSP programming. If things are done properly. That you can use a resistor to isolate the PIC from other circuits during programming
     
  7. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    470 Ohms is too low for ICSP. Maybe it can work! I don't recommend. Or you can make the LED display "high-Z" during ICSP.
     
  8. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    I am currently using a pickit 2 with a Pic16F887, I have RB7 connected to a 3904 transistor with a 220 ohm resistor, I also use this pin for debug, and it does not affect anything..... if all you have is an LED on he other end of the resistor coming off of RB7 or RB6, your setup should be adequate......
     
Loading...