question about write program memory

[Fabri]

Hi to All,

I've a strange situation with PIC16F877A returned back from over 100 hours of work. On part of software doesn't work and I suppose depend from microcontroller because changed it all work fine. Ther's no any problem in hardware.

I belive something happend to program memory but I can't verify it because the micro i protected from reading.
There's no bootloader or other routine writing program memory in software.

Is there any way to verify program memory ?

Does possible the micro write program memory instead eeprom ?

Have you got to suggest me ?

thanks for replay

[Ttelmah]

If write protection is enabled, then the micro could not write it's program memory. The question is what protection mode you had got turned on?.
You can write a chip, turn on the protection, and read it. The you get back, will be the same for any chip, given the same code is loaded. Use this data to verify the faulty chip. Where the verification fails, will show which cell(s) are involved.

Best Wishes

[Fabri]

Hi,

I have all configuration bit in ON except low voltage program.

So there's no possibility to read eeprom o program memory.

[Ttelmah]

Basically, if you program a chip, and enable the read protection, you can still read the chip, but get back encrypted data. So the recommended way to verify a protected chip, is to program it with the protection 'off'. Verify that the code is working, and then enable the protection. Then read the chip. You will now get back the _encrypted_ data, for a known 'good' chip and program. Then when you program future chips with the same program (and protection 'on'), you can perform a verification against the encrypted data. This will still work, and still tell you where the verification fails. Some production programmers have an automated mode to support this.

Best Wishes

[Fabri]

Hi Ttelmah,

I use ICD2 Microchip as in circuit programmer and when I read protected chip it doesn't show anything in program memory mask.

Is there anyway to read protected chip with ICD2 ?

Regards,
Fabri