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PICList Thread
'16F876, LVP bit and RB3 pin...'
2000\03\12@052419 by Antonio Pasini

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I must draw a schematic *before* having some chips to play with... so, I
hope you PIClisters could give me an hand...

Reading the datasheet, I understand that enabling LVP (which is on by
default) I can re-program the 16F876 in circuit, without
apllying Vhh on the /MCLR pin. But I loose RB3.

But... given that I can firstly program the micro with "normal" (high
voltage) In Circuit Serial Programming, I'd insert a serial flash
loader.

When the 16F876 reprograms itself via an UART connection, executing its
internal "flash loader" code, must the LVP bit be set ?
Have I to give up to RB3 pin ? I'd power the micro with standard 5V,
however..

I suppose so, 'cause the micro needs to re-program its flash cells,
without external Vhh high voltage, but I'd like a confirm...

what do you think about it ?


Another related question... I purchased MPLAB-ICD. In production,
however, we were used to program
DIP parts on a standalone programmer. It programs 16F876.

Now, going on SMT parts... I'd like to continue using standalone
programmer...

My thought was to bring /MCLR, GND, VDD, RB6, RB7 wires from the ZIF
socket of my programmer, and bring them with a short
cable to my board.

I read somewhere that standalone programmers use the same pins for ICSP,
on the 16F876... could it work ?

2000\03\12@063507 by mike

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On Sun, 12 Mar 2000 11:21:09 +0100, you wrote:

>I must draw a schematic *before* having some chips to play with... so, I
>hope you PIClisters could give me an hand...
>
>Reading the datasheet, I understand that enabling LVP (which is on by
>default) I can re-program the 16F876 in circuit, without
>apllying Vhh on the /MCLR pin. But I loose RB3.
>
>But... given that I can firstly program the micro with "normal" (high
>voltage) In Circuit Serial Programming, I'd insert a serial flash
>loader.
>
>When the 16F876 reprograms itself via an UART connection, executing its
>internal "flash loader" code, must the LVP bit be set ?
No
>Have I to give up to RB3 pin ? I'd power the micro with standard 5V,
>however..
The LVP allows external in-circuit programming without a high voltage.
Has no effect on 'internal' self-programming mode.

2000\03\12@070244 by Byron A Jeff

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>
> I must draw a schematic *before* having some chips to play with... so, I
> hope you PIClisters could give me an hand...

OK.

>
> Reading the datasheet, I understand that enabling LVP (which is on by
> default) I can re-program the 16F876 in circuit, without
> apllying Vhh on the /MCLR pin. But I loose RB3.

Both of these assertions are correct.

>
> But... given that I can firstly program the micro with "normal" (high
> voltage) In Circuit Serial Programming, I'd insert a serial flash
> loader.

Like Tony Nixon's RomZAP. It can be installed with either the LVP or a
"normal" HVP ICSP.

>
> When the 16F876 reprograms itself via an UART connection, executing its
> internal "flash loader" code, must the LVP bit be set ?

No. You can reset it when you program the ROM loader.

> Have I to give up to RB3 pin ?

Nope. Once the LVP bit is reset RB3 reverts to normail operation.


> I'd power the micro with standard 5V,

That's fine.

> however..
>
> I suppose so, 'cause the micro needs to re-program its flash cells,
> without external Vhh high voltage, but I'd like a confirm...

The micro uses 5V external to reprogram the cells. I think it has an internal
voltage converter. Even with HVP the Vpp is just a signal to indicate that
programming is to occur, not a voltage actually applied to the cells.

>
> what do you think about it ?

A 5V only system with LVP reset can be reprogrammed by a ROM loader and regain
the normal operation of RB3. The only debate at this point is that a serial
port loader is the easiest to implement and you'd have a redirect the internal
UART for loading. A very minor issue IMHO.

BAJ

2000\03\12@072604 by mike

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>A 5V only system with LVP reset can be reprogrammed by a ROM loader and regain
>the normal operation of RB3. The only debate at this point is that a serial
>port loader is the easiest to implement and you'd have a redirect the internal
>UART for loading. A very minor issue IMHO.
>
I don't think this is true. My understanding is that LVP (or any of
the config bits) cannot be programmed in self-program mode, and once
LVP is disabled it can only be re-enabled using high voltage on MCLR.

2000\03\12@105550 by Byron A Jeff

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>
> >A 5V only system with LVP reset can be reprogrammed by a ROM loader and =
> regain
> >the normal operation of RB3. The only debate at this point is that a =
> serial
> >port loader is the easiest to implement and you'd have a redirect the =
> internal
> >UART for loading. A very minor issue IMHO.
> >
> I don't think this is true. My understanding is that LVP (or any of
> the config bits) cannot be programmed in self-program mode, and once
> LVP is disabled it can only be re-enabled using high voltage on MCLR.=20

Mike you misinterpreted what I was trying to say. I was trying to say that
self-programming mode only requires 5V whether or not LVP is set or not.

You are correct in pointing out that self-programming only allows for
rewriting program memory, not config memory.

Also I don't think I did a real job job on that last statement. What I was
trying to say is that typically a self-programming boot loader would use
the onboard UART and that you'd have to have some way to separate UART
usage for programming and UART usage for normal use.

BAJ
>

2000\03\13@161008 by Dwayne Reid

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<x-flowed>At 11:21 AM 3/12/00 +0100, Antonio Pasini wrote:
>I must draw a schematic *before* having some chips to play with... so, I
>hope you PIClisters could give me an hand...
>
>Reading the datasheet, I understand that enabling LVP (which is on by
>default) I can re-program the 16F876 in circuit, without
>apllying Vhh on the /MCLR pin. But I loose RB3.
>
>But... given that I can firstly program the micro with "normal" (high
>voltage) In Circuit Serial Programming, I'd insert a serial flash
>loader.

Tony Nixon's ROMzap utility does NOT require LVP programming.  ALL pic pins
are available to you except the two serial pins (RC6, RC7) which need to
connect to a MAX232 (or similar interface).  Note that the serial port is
available to your program and for your use anytime the '876 is not being
programmed.  But you have to connect the serial port to your PC when you
want to load a new program into the '876.

You do have to use a standard programmer to program the '876 the first time
(to put the boot loader in).

dwayne



Dwayne Reid   <spam_OUTdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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