Hi Richard,

You probably have something like this at the start of your source code.

;
    Title "Man, I wish I knew how this PIC works"
;
    list P = 16F876
;
    include "P16f876.inc"

I am assuming nothing special for your project so this FUSE setting
should be OK for your purposes. Just copy this into your source after
the above.

;
; ------------------
; CONFIGURATION FUSE
; ------------------
;
    __CONFIG _CP_OFF & _WRT_ENABLE_OFF & _HS_OSC & _WDT_OFF & _PWRTE_OFF
& _BODEN_OFF & _LVP_OFF & _CPD_OFF & _DEBUG_OFF

NOTE: that ALL of this __CONFIG statement must be on a single line.

Wouters WISP programmer will see the FUSE data in the HEX file after you
assemble it ready for programming and will automatically write to the
FUSE register in the PIC according to the settings listed above.


There are 2 modes to programming this chip. High voltage where around
13V is needed on the MCLR pin, and low voltage mode (LVP) where only 5V
is needed on the MCLR pin, but in this case RB3 is also used. If the
WISP is not using anything connected to RB3, then you are using HV mode
and don't need LVP enabled.

If you have LVP mode enabled, then the RB3 pin should be tied low. If
this pin is allowed to float unconnected or go HI, the PIC may
inadvertantly go into programming mode, and you may think something is
wrong with your code or circuit when the chip does not work as expected.
Very frustrating.

The above FUSE statement has LVP_OFF and disables LVP programming mode.

You will be able to use RB3 as a general purpose IO pin with LVP disabled.

LVP mode is enabled by default on a blank chip.

regards

Tony

Richard S wrote:

>Hi Tony:
>
>I don't know how to dissable the LVP but if I do I am concerned that my WISP628 in circuit programmer will not be able to progam the chip anymore once I dissable the LVP. I think for the 16f876 the programmer is not using the LVP but is using the MCLR#  but not sure this is all still new to me. I disconnected the wire from my programmer that was connected to the RB3 pin and it still programs just fine with or without the 10K to ground but I did find a note on the wisp628 web site about putting this resistor in.
>
>So maybe it is safe to dissable the LVP bit. I think the 16f876 is self protecting if I read the specification correctly P134 of the data sheet. It looks like the only way to change the LVP bit is to do so in the HVP mode therefore the wisp628 (my in circuit programmer) must be programming in this HVP mode.
>
>Can someone please help me understand how to set the LVP bit I can see from the datasheet that its bit 7 of the "configuration word address 2007h".
>
>Thanks again
>
>
>

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