Sudden problem with MCLR on PIC16F628

[Futterama]

Hello,

I was just improving my PIC programmer hardware, and suddenly it seems like the MCLR pin is kept low on a PIC16F628 (short circuit inside the PIC?).

If I connect 12V to the MCLR, and GND to GND with no other pins connected (not even Vdd), heavy current will run through the MCLR pin (>250mA and probably more if my power supply didn't have current limit). The voltage on the MCLR pin will only rise to approx. 2V.

If I connect the PIC to 5V supply and GND (no MCLR connected) the program in the PIC will run fine.

What happened to the PIC?

If it makes a difference, the PIC was obtained as a sample from Microchip.

Regards,
Futterama

 

[Nigel Goodwin]

Hello,

I was just improving my PIC programmer hardware, and suddenly it seems like the MCLR pin is kept low on a PIC16F628 (short circuit inside the PIC?).

If I connect 12V to the MCLR, and GND to GND with no other pins connected (not even Vdd), heavy current will run through the MCLR pin (>250mA and probably more if my power supply didn't have current limit). The voltage on the MCLR pin will only rise to approx. 2V.

If I connect the PIC to 5V supply and GND (no MCLR connected) the program in the PIC will run fine.

What happened to the PIC?

You've destroyed it 8)

PIC's are extremely hardy devices, so you must have done something particularly 'nasty' to it - but sticking 12V from a PSU directly in the MCLR pin doesn't sound like you've treated it with much love or care?.

 

[Futterama]

Well, I think PICs are rough devices and I didn't do anything nasty...

Actually, there is a transistor between MCLR pin and the PSU, but does it make a difference? And I would never hurt my little babyes on purpose :lol:

 

[eblc1388]

Microchip's sample is just like an ordinary PIC that you buy from stores and would not self distruct after a certain time.

You might have connected a voltage higher than 15V to the MCLR pin and this could damage it.

Do not improve something if it ain't broken.

 

[aibelectronics]

reply

Well, I think PICs are rough devices and I didn't do anything nasty...

Actually, there is a transistor between MCLR pin and the PSUit

to amplify the current running to it i guess? Shocks! :shock: [/b]

 

[Futterama]

Re: reply

to amplify the current running to it i guess? Shocks! :shock:

No, to turn the Vpp on and off during programming.

The voltage at Vpp have been below 13V at all times (12.82 to be accurate).

I have to improve my programmer, so it can program other PICs than the 16F628 :wink:

Well, I guess this is what can happen. I'll leave it in the ESD safe box for a few weeks, and it will be ready to reprogram again :wink:

 

[eblc1388]

Re: reply

I have to improve my programmer, so it can program other PICs than the 16F628 :wink:

What "improvement" is needed to program other PICs than 16F628?

 

[Futterama]

The ability to control the Vdd.

 

[Nigel Goodwin]

The ability to control the Vdd.

The 16F628 requires that as well, although you can get along without it on many PIC's, while the 16F628 is acually one which it is more important on.

 

[Futterama]

My programmer works fine with PIC16F628 and a constant Vdd at programming cycle.

 

[Nigel Goodwin]

My programmer works fine with PIC16F628 and a constant Vdd at programming cycle.

Make sure you NEVER select the internal oscillator, or it won't!.

 

[Futterama]

Nigel, I ALWAYS use the internal osc and I have programmed the PIC16F628 MANY times with this simple programmer...

 

[Nigel Goodwin]

Nigel, I ALWAYS use the internal osc and I have programmed the PIC16F628 MANY times with this simple programmer...

And you're NOT switching Vdd?.

 

[Futterama]

And you're NOT switching Vdd?.

That's right, I'm NOT switching Vdd, and it still works.

 

[Nigel Goodwin]

And you're NOT switching Vdd?.

That's right, I'm NOT switching Vdd, and it still works.

So how do you select programming mode?, particularly if the PIC is already programmed to use the internal oscillator?.

 

[Futterama]

I didn't make the software used for programming (David Tait's FPP Flash PIC Programmer) so I don't know. The hardware only controls Vpp, data and clock. Vdd is applied at all times.

 

[Nigel Goodwin]

I didn't make the software used for programming (David Tait's FPP Flash PIC Programmer) so I don't know. The hardware only controls Vpp, data and clock. Vdd is applied at all times.

That's because it's an ICSP (In Circuit Serial programmer), as such it can pull MCLR (Vpp) down low to reset the PIC - normal (non-ICSP) don't usually have this capability.