Investigation of a Micro-controller

Thread Starter

cstroh

Joined Jan 16, 2019
82
In a continuing investigation of a driver board, can a rough evaluation of a micro-controller chip be done by testing each pin relative to the ground pin for resistance with the chip removed from the board? Am using an ohm meter with a max voltage of 1.4 volts. Could this test damage the micro-controller?
Here are the results of the test. The ground pin is pin 5 and the pin for normally supply voltage is pin 14. Attached is the document for the PIC16F628 micro-controller if needed.

Resistance Measurements with neg probe at Pin 5
(ohms)IC off board1.455 VDC
U14PIC16F628-047P
PinohmsPinohms
1​
0​
18​
500​
2​
500​
17​
500​
3​
infin
16​
500​
4​
infin
15​
500​
5​
14​
350​
6​
500​
13​
infin
7​
500​
12​
50​
8​
500​
11​
500​
9​
500​
10​
500​
 

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jpanhalt

Joined Jan 18, 2008
9,710
It remains unclear what you are trying to determine. Why not just attach the chip to your programmer and erase it or read it (if not protected).
 

Thread Starter

cstroh

Joined Jan 16, 2019
82
The 50 ohms also looks bad to me. As to "attach the chip to your programmer" I am headed in that direction but presently do not have a programmer. I also suspect that the code will be protected but hope not.
 

Thread Starter

cstroh

Joined Jan 16, 2019
82
So the 0 at pin 1 is definitely a problem. Can you shed any light on what I need to do to see if the chip program is protected?
 

jpanhalt

Joined Jan 18, 2008
9,710
The only way I know is to connect it to a programmer.

That pin (#1) may not be a problem, if you attach the ICSP pins out of the circuit. Years ago, I programmed and used a similar chip with a bad pin. Just don't connect that pin directly to Vcc.
 

Thread Starter

cstroh

Joined Jan 16, 2019
82
When you speak of a programmer, is this a board specifically to program this chip or just what does this programmer look like?
 

Thread Starter

cstroh

Joined Jan 16, 2019
82
I downloaded the Microchip MPLAB X IPE & IDE and am about to buy their DM164137 curiosity board which is designed for 8. 14 and 20 pins. The PIC16F628 is 18 pins and not sure whether this can be made to work.
 

jpanhalt

Joined Jan 18, 2008
9,710
ICSP (In Circuit Serial Programming) uses three pins plus GND and VSS. The three are Data, Clock, and VPP (for HV programming -- HVP). The latter puts the chip into programming mode. That chip also allows low-voltage programming (PGM pin), but that can be turned off. HVP always works.

I would get a PicKit 2, 3, or 4. Put the chip on a bread board, and use that. MPLab X will work. I use MPLab 8.92, as I haven't taken the time to learn MPLab X and only program in Assembly. If the chip is not read protected, you can easily convert the downloaded code to Assembly.
 

Thread Starter

cstroh

Joined Jan 16, 2019
82
I can get the PicKit3 and adaptor which I suppose enables me to do all this without having to mount the chip on a board? And this can be done with just plugging the chip into the adaptor? Am I correct with this information?
 

jpanhalt

Joined Jan 18, 2008
9,710
As I mentioned, there are only 5 wires to connect. The pinouts on chips vary. The advantage of an adapter kit is that the changes needed for the different pinouts are made with those little 2-pin jumpers. On a bread breadboard, you have to change your jumpers.

I would use a breadboard with a ZIF socket for just a few. For more, I got this adapter kit: https://www.ebay.com/itm/ICSP-Adapter-ZIF-Kit-PIC-use-with-PICkit-2-3-or-4/231507323729?hash=item35e6e96b51:g:N~UAAOSw-7RVB1aM

There are many others on eBay. I also suggest genuine Microchip products. There are lots of copies, some work better than others, but Microchip supports its products.

The PK3 will do almost all chips except the very old OTP chips and some very new ones. I don't know the cutoff for the latter. The PK4 does all the latest, but I am not sure how early it goes. The PIC16F628A was very common, and although older, I suspect almost anything will support it.
 

atferrari

Joined Jan 6, 2004
4,008
At your level of knowledge, evident by the OP, I cannot imagine what could be your conclusions by measuring the pins as described. Nothing like a functional test for starters... and even then.
 

peterdeco

Joined Oct 8, 2019
185
You cannot determine the functionality of a PIC with an ohmmeter. It has program memory, internal registers, ADC's, PWM,s etc. that can fail and cannot be measured externally. We have even had internal programs get corrupted on a good PIC. It was erased, reprogrammed and worked fine. Possibly due to static, voltage spike, etc. Another faulty PIC had 4 ADC's and only 3 worked.
 

AlbertHall

Joined Jun 4, 2014
10,022
You cannot determine the functionality of a PIC with an ohmmeter. It has program memory, internal registers, ADC's, PWM,s etc. that can fail and cannot be measured externally. We have even had internal programs get corrupted on a good PIC. It was erased, reprogrammed and worked fine. Possibly due to static, voltage spike, etc. Another faulty PIC had 4 ADC's and only 3 worked.
Many PICs can write to their own flash so if they 'go bonkers' then the program could get corrupted.
 

Thread Starter

cstroh

Joined Jan 16, 2019
82
I agree. But if I get short circuits between ground and any pins, why would I continue to pursue evaluating functionality?
 
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