Can one determine Chip ID (16F62xA/16F648A)

[dman66]

Hi all,

Right now my code is less than 2K so it fits in either a 16F628A or a 16F648A. About half of our boards were populated with 16F628A and the other half with 16F648A.

At runtime is there any possible way to know which part I'm running on?

GETENV() appears to be mainly compile time (i.e. DEVICE, PROGRAM_MEMORY, etc.)

I know on the 16F877, for instance, I can use read_program_memory(). This call doesn't work on the 628A/648A.

Any other ideas?

dman

[PCM programmer]

I think you can only read the Device ID when those PICs are in program
mode. You can't do it with user code at runtime. Here is one way that
might work:

The RAM memory map for the 16F628A is different from the 16F648A,
with respect to Bank 2. The smaller PIC has a hole in the bank 2 RAM,
from addresses 0x150 to 0x16F. The 16F648A doesn't have a hole
there -- it has RAM. According to the data sheet, if you try to read the
RAM in that address range in the 16F628A, you will read 0's.

So you could do a simple test. Try to write 0x55 to RAM address 0x150.
If you read back 0x55, then you have a 16F648A. If you read 0x00,
then you have a 16F628A. If you read something else -- I'm not sure,
maybe it's a bad chip. You will need to decide what to do in that case.

You can use the #locate directive to declare a test variable.

[dman66]

This is brilliant - I thought about that too, but didn't realize that unimplemented RAM in the 627A/628A would return 0.

I tried it out and it works like a charm

Thanks!