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'[PIC]: ICSP on 16F628 and MCLR'
2002\07\11@150736 by Richard Mellina

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       I'm new to pics and need some help on a project I'm working on. Can I do
ICSP on a 16F628 if MCLR is internally tied to Vdd? Or does it matter when
programming? Any help would be greatly appreciated.

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2002\07\11@154534 by Byron A Jeff

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On Thu, Jul 11, 2002 at 02:03:17PM -0500, Richard Mellina wrote:
>I'm new to pics and need some help on a project I'm working on. Can I do
> ICSP on a 16F628 if MCLR is internally tied to Vdd?

Yes. From my testing if MCLR is defined as internal, then power cycling Vdd is
the mechanism for causing an ordinary reset.

> Or does it matter when programming?

The programming cycle is unchanged. For high voltage programming (HVP), the
trigger has always been Vpp on MCLR rising to 3.5V above Vdd. For low voltage
programming, the programming pin is attached to RB4 which must be grounded
for ordinary operation. In neither case will programming mode be entered
usless explictly triggered, in which case programming mode is entered as
normal.

>Any help would be greatly appreciated.
>

The bottom line is that you can treat the PIC16F628 as normal even when
MCLR is set to internal. However you've missed the real problem which I'd
like to put on the table: If one is using a HVP ICSP programmer and has
MCLR set to internal, then how does one use the input for ordinary uses
when 13V will be dropped on the line when programming? Short of using it
for a switch, or interfacing a transistor/diode, how can one connect ordinary
logic to the pin?

It's currently an intellectual exercise with me because I'm only doing LVP at
the current time. But I was wondering...

BAJ

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2002\07\11@161207 by Olin Lathrop

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> However you've missed the real problem which I'd
> like to put on the table: If one is using a HVP ICSP programmer and has
> MCLR set to internal, then how does one use the input for ordinary uses
> when 13V will be dropped on the line when programming? Short of using it
> for a switch, or interfacing a transistor/diode, how can one connect
ordinary
> logic to the pin?

Usually you don't.  I've done this with a diode and a pulldown resistor.


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2002\07\11@182248 by Bob Ammerman

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>         I'm new to pics and need some help on a project I'm working on.
Can I do
> ICSP on a 16F628 if MCLR is internally tied to Vdd? Or does it matter when
> programming? Any help would be greatly appreciated.

ICSP works even if the "MCLR" pin is defined to be a normal I/O pin.

Bob Ammerman
RAm Systems

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2002\07\11@183810 by Lyle Hazelwood

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----- Original Message -----
From: "Bob Ammerman" <spam_OUTrammermanTakeThisOuTspamADELPHIA.NET>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Thursday, July 11, 2002 3:15 PM
Subject: Re: [PIC]: ICSP on 16F628 and MCLR


> >         I'm new to pics and need some help on a project I'm working on.
> Can I do
> > ICSP on a 16F628 if MCLR is internally tied to Vdd? Or does it matter
when
> > programming? Any help would be greatly appreciated.
>
> ICSP works even if the "MCLR" pin is defined to be a normal I/O pin.
>
> Bob Ammerman
> RAm Systems

MCLR may be defined for other uses if you don't need a hardware reset
at run time, however..
If MCLR is tied directly to VDD, raising it to VPP will raise VDD to about
13 volts across the board. This could be bad for the PIC, and any other
chips that happen to be sharing the (usually +5Volt) VDD line.
It could also require more current than many simpler programmers can
provide.
Unless I misunderstand the question??
Lyle Hazelwood

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2002\07\11@190707 by Bob Ammerman

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By "internally connected to Vdd" the OP really meant "use the MCLR pin as an
ordinary input and use the internal MCLR functionality of the chip.".

Bob Ammerman
RAm Systems

{Original Message removed}

2002\07\12@033145 by Alan B. Pearce

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>The bottom line is that you can treat the PIC16F628 as
>normal even when MCLR is set to internal. However you've
>missed the real problem which I'd like to put on the
>table: If one is using a HVP ICSP programmer and has MCLR
>set to internal, then how does one use the input for
>ordinary uses when 13V will be dropped on the line when
>programming? Short of using it for a switch, or interfacing
>a transistor/diode, how can one connect ordinary logic to the pin?

>It's currently an intellectual exercise with me because I'm
>only doing LVP at the current time. But I was wondering...

This sounds rather like a case of you loose a pin either way :)

MCLR if you HVP, or RB4 if you LVP. :((

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2002\07\12@082820 by Byron A Jeff

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On Fri, Jul 12, 2002 at 08:29:51AM +0100, Alan B. Pearce wrote:
> >The bottom line is that you can treat the PIC16F628 as
> >normal even when MCLR is set to internal. However you've
> >missed the real problem which I'd like to put on the
> >table: If one is using a HVP ICSP programmer and has MCLR
> >set to internal, then how does one use the input for
> >ordinary uses when 13V will be dropped on the line when
> >programming? Short of using it for a switch, or interfacing
> >a transistor/diode, how can one connect ordinary logic to the pin?
>
> >It's currently an intellectual exercise with me because I'm
> >only doing LVP at the current time. But I was wondering...
>
> This sounds rather like a case of you loose a pin either way :)
>
> MCLR if you HVP, or RB4 if you LVP. :((

Quite true, at least in the ICSP scenario. Of course if the you use the
internal RC oscillator, you can convert the two OSC pins into general purpose
I/O pins.

BAJ

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