PIC problem !!!

[Rony]

Hi all,

I wrote a program using PBP250C for the 16F877A
i am using the ICSP to program the PIC, everything is working properly, i can write and read the PIC, but sometimes when trying to read the program via the ICSP, after reading it, the PIC stops running and i should reprogram it again, as if it becomes erased !!!
i don't know what's happening, the hardware is correct, it is not the first time that i am using the ICSP, i can share the PCB if it is necessary.

Anyone can help ???
Thank you

[cncmachineguy]

Maybe it's a MCLR issue?

[rsocor01]

Rony,

There are many things that can cause that problem. If we can see the schematics it would help. There is some help here for the melabs programers,

http://melabs.com/support/icsp.htm

[Rony]

This is the PCB capture, thanks

[Rony]

With "DIP Switch"

[Rony]

PORTB is internally puled up,
i switched ON pin 4 in the DIP switch (RB3 to zero) and still having the same problem

[Jumper]

Hi,

I have never liked the 16F877A pic. When I used it I always had resets and other strange issues so I just changed to 18F452 or 18F4620 which are both pin-compatible with the 877A and not that much more expensive.

Just make sure the LVP (low voltage programming) is turned off in the config bits.

Sometimes I rather have a working product than really understanding why it doesnt work.

[Acetronics2]

Hi,

With the BIG caps on your board something Hurts me :

14.5 Power-on Reset (POR)
A Power-on Reset pulse is generated on-chip when

V

DD rise is detected (in the range of 1.2V-1.7V). To take

advantage of the POR, tie the MCLR pin to V

DD

through an RC network, as described in

Section 14.4

“MCLR”

. A maximum rise time for VDD is specified.

See

Section 17.0 “Electrical Characteristics” for

details.
When the device starts normal operation (exits the
Reset condition), device operating parameters (voltage,
frequency, temperature, etc.) must be met to
ensure operation. If these conditions are not met, the
device must be held in Reset until the operating conditions

are met.

looks there's a missing cap in your design ... don't you think ???

On my side, I use MC34064P5 supervisor to get rid of power on or reset rise times ... and have NO issues with reset pin ...

BTW ... a hardware reset after reading the Prog memory is not to forget ...

Alain