12F675 won't reprogram or erase

[modifyit]

I appreciate the suggestion, I can throw away the chip and resolder a new one on, but I want to figure out how to keep this from happening again. I have killed 2 chips already and I know every other one I program will be dead unless I change something.

Do you know if the MELABS programmer will automatically skip the OSCAL and BandGap settings? I need to program 1000s of these once i get this figured out and can't afford the time of writing down the OSCAL values of every chip.

I am not even sure the OSCAL value being deleted is the problem, as I understand it I should still be able to reprogram the chip if that were the case and the internal oscillator would just be off by a little. At this point the programmer won't let me reprogram or erase the chip.

[Melanie]

OSCAL and bandgap are unimportant in making your PIC work.

When you ERASe, all you ERASE is the program codespace and perhaps the EEPROM, the CONFIG settings are untouched.

Just write a simple LED Blink Program for Internal Oscillator and Internal MCLR (ie MCLR as an I/O (Input) pin) and burn that into your PIC. You'll probably find it works.

[modifyit]

That's what I thought Melanie but when I tried that the chip locked up and won't allow for an erase or a reprogram.

Should it matter that I have a 5k pull-down resistor on the MCLR pin since I am using it as an input? I think I also have 5k pull-downs on the ICSPData and ICSPCLK pins also.

I'm starting to think this is more of a schematic issue then a config issue.

Thanks again for any thoughts, they are much appreciated

[Bruce]

Programming in-circuit can be tricky is you have Vpp, data and clock pins tied to the application circuit.

Programming voltage on /MCLR needs to rise fast enough to prevent the program counter from incrementing. If it does not rise fast enough, your code previously programmed into the device can start executing, and it screws up the whole process. In this case, you're trying to program a PIC that's already executing code, and is no longer in program mode.

The internal RC osc makes the start-up process even faster, so it's even more critical for Vpp to rise fast.

Try lifting the pull-down resistor you have on /MCLR, and make sure you have the programming clock & data pins disconnected from any external loads.

External loads on data & clock pins will also screw up ICSP.

That should allow you to re-program & erase in-circuit without any problems assuming the PIC isn't dead.

[modifyit]

I'll give that a shot, but that basically means taking the pic out of the circuit using jumpers or I will loose 3 of the 6 GPIOs. I thought the pic should be able to handle this, I will try pulling the MCLR pull-down off first to see what that does and go from there. If the program programs the first time, should the clock and data pins really matter?

Thanks

[Bruce]

Yes the clock & data pins definitely matter if you program in-circuit. A load on the clock pin in particular will really mess with timing.

Read Microchips' DS91017B ICSP guide for a detailed explanation.

[Ron Marcus]

Yes the clock & data pins definitely matter if you program in-circuit. A load on the clock pin in particular will really mess with timing.

Read Microchips' DS91017B ICSP guide for a detailed explanation.

I had the same issue rear it's ugly head some months back. If your code is evolving, you really should keep MCLR as a reset. The last programming action will be to flip the config fuse for the MCLR pin to become an input. If you place a 1 K resistor between the clock pin and the circuit it is attached to, this will help. Same with Data pin. For ICSP, I raise the pullup resistor to MCLR to 22K. It helps when your power supply is 2 to 3 volts and the programming power is 5 volts. If that's not enough, a schottky diode from B+ to the VDD pin will allow ICSP in a circuit that can't take 5 volts. I fried come 3 volt comm chips this way before the stupid light went off!
I perconally traded the 12F series for the 16F690 in the 4 mm package. 18 GPIOs and 4 K of flash memory!Boy is this living!

[modifyit]

Well I figured out the issue, not the solution but the issue.

I completely isolated the chip and it would still not program so, I went ahead and replaced the chip and it programmed fine. I got pin GP.2 blinking an LED so that was successful.

Still leaving the MCLR, ICSPDat and ICSClk isolated I decided to try and toggle pin GP.1

As soon as I do this the my MELabs throws a Config error while programming and the chip becomes useless, no programability or eraseability just like my first post.

Any clue why the board is doing this? Here is a snipit of my code

[code\]
DEFINE OSCCAL_1K 1
' Config Fuses
@ __config _INTRC_OSC_NOCLKOUT & _CPD_ON & _CP_ON & _BODEN_ON & _MCLRE_OFF & _PWRTE_ON & _WDT_ON

' Variable Definitions
LED VAR GPIO.1

blink var bit


CMCON=7
TRISIO=%11111001 ' Input 0,3,4,5 Output 1,2
ANSEL=0

Main:
blink=blink+1
led=blink
pause 100
goto main

[\code]


If I change this code to apply to pin GP.2 it works fine and will reprogram all day long

Thanks for any help