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.

 

for LEDs you need at least 2.2K Ohm. IC input does not need protection (from RB6/RB7).

 

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

thanks in advanced

 

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.

 

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).

 

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

 

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).

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.

 

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......