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Using the PGD and PGC pins

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UTMonkey

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Hi All,

Sorry for the newb question, but I am writing some LCD code and am thinking of connecting the DB7-DB4 pins of the LCD to RB2-RB6 of my 2550 (love the chip by the way!).

This would mean using the PDG\PGC pins of the 2550, would I still be able to program or debug? are there any considerations when using these pins?

Thanks in advance.

Mark
 
I would consider using a couple of jumpers in order to isolate the programming lines from the application circuit when you program the PIC.
 
Hi Mark,

Db7-4 to rb2-6 - 4 to 5 ?

Debugger needs the dedicated use of rb6 and rb7.

The programmer also need rb6 and rb7 either via some isolation circuitry or a simple double pole switch.

Am I right in thinking that you are using rb0,1,2 for the three control lines ? - if so then why not just use two - its not necessary for simple applications to use the R/W pin 5 of the lcd, which is taken to 0v and your code amended to suit.
 
Yes add a header on PGD and PGC, because even with a LED across those pins it will not want to program it.
 
For your development work, why not use the 40pin 4550 chip.
You can dedicate Rb6,7 to the programmer /debugger - no switches etc.
Makes testing so much easier - instant programming from Mplab etc - when you program is complete just re-port it onto the 2550.
 
Everything said here is good. If you still want to share the pins with the LCD use B6 and B7 for input only pins on the LCD. Maybe CLK and R/W. There is a chance that input only pills will always present a high impedance and not interfere with the ICSP.

May be worth a try.
 
I have used the whole of port B to drive a GLCD using a 16F886. I placed 1k resistors in the clock and data connections between the ICSP header and the rest of the circuit. With this arrangement, you can't debug but can program. You also have to compile the release version.

Mike.
 
UTMonkey said:
Hi All,

Sorry for the newb question, but I am writing some LCD code and am thinking of connecting the DB7-DB4 pins of the LCD to RB2-RB6 of my 2550 (love the chip by the way!).

This would mean using the PDG\PGC pins of the 2550, would I still be able to program or debug? are there any considerations when using these pins?

Thanks in advance.

Mark

It shouldn't prevent you from debugging, but you lost the pin when you are in the debugging mode.
 
Thanks to all, as I am still a newbie at all this I like the comfort of debugging, the notion of using the 4550 is pretty good (I have a few of the LF variety).

I think I will put the LCD DB (4 bit) lines on RA0-RA3.

Thanks again for the advice.

Mark
 
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