Adding ICSP

[Joel Rainville]

I want to add ICSP support on Nigel's tutorial development boards.

I need to isolate the circuit from Vpp with a diode. Is there an alternative to a schottky diode that will apply 5V to MCLR to enable the target PIC?

I'd really like to not lose RB6 & RB7 to ICSP. Can I use a similar technique with 2 diodes connected to each pin with opposite polarities to allow ICSP *and* I/O on RB6/PGC & RB7/PGD, or would this mess the programming signals too much?

The ICSP guide from Microchip doesn't give much details on this...

 

[Nigel Goodwin]

My tutorial designs don't use ICSP because it's so limiting, and complicates the design so much. If you mount your PIC in a turned pin socket (as I do) it makes it so simple to remove and reprogram (with no possibility of damaging the PIC pins), that it makes the advantages of ICSP not worth bothering with.

 

[pittuck]

have the MCLR pin as normal, but with a 10k pull up, works fine, no diode needed...

Next, the pins, what are you using them for? can u put a switch in? or jumpers?

 

[Joel Rainville]

Hey pittuck,

have the MCLR pin as normal, but with a 10k pull up, works fine, no diode needed...

Isn't this dangerous for my 5V Vdd supply? Won't current flow backwards when my programmer applies Vpp?

Next, the pins, what are you using them for? can u put a switch in? or jumpers?

I'm building Nigel's tutorial boards. I'd like to use pins RB6/RB7 for the basic driving of LEDs and general CMOS logic levels. I'd like a flexible way that would allow me the full use of PORTB's 8 bits in most circumstances.

I'm starting to realize this is no small task, and that I'm looking at ICSP from a hobbyist point of view. Jumpers/switches make sense in an industrial/commercial application where infrequent updates can be applied. But using these on devboards kinda defeats the point of even trying ICSP in the first place. If I have to mess with jumpers, might as well get the chip out, and put it in my programmer...

I'd like a plug & play solution, where I can operate everything with just mouse clicks Maybe what I'm looking for is a bootloader here. But that'd just be moving the problem to other pins.

 

[pittuck]

only a very small ammount (0.0009A -> 0.9mA as i calculate).

More info here -> **broken link removed**

 

[Joel Rainville]

only a very small ammount (0.0009A -> 0.9mA as i calculate).

More info here -> **broken link removed**

Thanks.

I find it weird that while that schematic shows a schottky on Vdd, there's nothing pulling MCLR up on the target circuit. It looks like the PIC is programmed with "MCLR Enable", or the programmer stays connected permanently and is used to reset the PIC? Am I missing something?

In fact, I never even thought of having the programmer switch Vdd. I was thinking of having the PIC powered by the target circuit, and just connecting PGC, PGD and MCLR (and obviously GND).

 

[Nigel Goodwin]

Maybe what I'm looking for is a bootloader here. But that'd just be moving the problem to other pins.

Many PIC applications use a serial port, so you often have an RS232 connection to a PC, this makes a bootloader the obviously choice in those circumstances.

 

[Joel Rainville]

Maybe what I'm looking for is a bootloader here. But that'd just be moving the problem to other pins.

Many PIC applications use a serial port, so you often have an RS232 connection to a PC, this makes a bootloader the obviously choice in those circumstances.

Yeah, I think that's the best solution for bigger PICs.

I am also building a board for the 8 pins 12F683 and its bigger cousins, the 14 pins 16F684/16F688. I think I won't bother with ICSP or bootloaders there...