Max/232 Bootloader problems - Schematic attached...

[Pic_User]

Hi Ross,

I left off a pull-up resistor on MCLR for that chip... it will be rectified later.

Bingo!
-Adam-

[rossfree]

Thank you for replying...

I am not having trouble with the breadboard. It's my new circuit board that does not allow me to program the chip. On the breadboard, I can program just fine.

I do have a pull-up resistor on the circuit board for the 876. I will have to add one for the 16f88 when I start working with that part of the circuit board.

The circuit board has a jumper that allows me to chose which PIC I am programming. Both will have the "bootloader" programs in them.

[Pic_User]

Hi Ross,

It's my new circuit board that does not allow me to program the chip.

You may have to post pictures of your PCB.

Did you etch it yourself?
Double sided?
Does it have plated through holes?
Are there any solder bridges?
Did you accidentally lay it out as a “mirror image”?
Are all the PCB parts installed with correct polarity?
Are external wires attached to the correct places?
Is the MCLR resistor really 4.7k not 4.7 Ohms (4k7 not 4R7)?

A picture is worth a thousand questions!

-Adam-

[rossfree]

To Pic_User,

Thank you for your reply.

Did you etch it yourself? No... PCB123. I made two boards. No solder-mask or SS. And I found a problem earlier... my metal can crystal was intermittantly touching traces under it. Ha! Fixed.

Double sided? Yes.

Does it have plated through holes? Yes.

Are there any solder bridges? I've been over it carefully. Can't find any. Doesn't mean I didn't miss something. But it's not a huge board. I've checked voltages and ohm'd pins. Nothing stands out as blatantly wrong. Power supply is cool, no hot parts at all. 5 volts where expected. 12 volts where expected... etc.

Did you accidentally lay it out as a “mirror image”? Nope.

Are all the PCB parts installed with correct polarity? Silk screen was wrong on LEDs... put them all in backwards. Bother! :-) I corrected it earlier.

Are external wires attached to the correct places? No external connections as yet. Only power supply, Max232, 876, and T/C amp on board. Trying to get this going before pushing on. One thing at a time. :-)

Is the MCLR resistor really 4.7k not 4.7 Ohms (4k7 not 4R7)? Good question... I checked it earlier. It is correct. And the 100 ohm resistor on pin 9 is correct also.

If I had pics of the board I would post. I'm including a PDF of the artwork and traces. Blue traces on bottom of board... Red on top.

I have three operator push buttons and a POT on back side of board and an in-line connector strip for the LCD (also on back of board). The LCD is not connected. And I have not put the operator POT on the board yet either (R23).

I know it is unlikely that you can do much... but just maybe someone will catch something I missed.

HELP HELP HELP! :-)

Thank you!!!

[skimask]

Do you have 16F876 or 16F876A selected in your programmer, or which chip do you have?
It's a thought...
How about the PGM pin on the '876? Do you have the right pullup/pulldown on that? Are you using high voltage on the breadboard and low voltage on the PCB?

[rossfree]

Do you have 16F876 or 16F876A selected in your programmer, or which chip do you have?

I'm using a 16f876. Microcode Studio is also set to 16f876.



It's a thought...
How about the PGM pin on the '876? Do you have the right pullup/pulldown on that? Are you using high voltage on the breadboard and low voltage on the PCB?

I am holding MCLR high with a 4.7k resistor. I don't think I need to do any more than that. I am using a MAX232 connected to TX and RX and pin 9 of the MAX is connected thru a 100ohm resistor to MCLR on the chip.

It asks for a reset when I try to program... but pressing the reset button on my circuit board does nothing for programming the chip... it does pull pin1 of the 876 (MCLR) from 5vdc to gnd.

I'm still checking voltages... and the thing that sticks out is that the voltages on the MAX232 on my circuit board are different from those on my breadboard. And all of this works on my breadboard... using the same MAX232 and the same 876. :-[

One voltage that really stands out is on pin 8 of the MAX232. On my breadboard... with the serial cable plugged in (from my computer) and the breadboard powered up, I read -10vdc. On my circuit board... under same conditions, it reads 0vdc. There is something wrong there. I will look at it closer.

If you haven't had a chance to look... I've posted a schematic and board layout in this thread.

Thank you for helping out!

Still looking for an answer.

Ross

[skimask]

I am holding MCLR high with a 4.7k resistor. I don't think I need to do any more than that. I am using a MAX232 connected to TX and RX and pin 9 of the MAX is connected thru a 100ohm resistor to MCLR on the chip.
Ross

Not MCLR-------PGM different pin, different function. It'll cause programming problems depending on method used to program.