Searching \ for '[PIC]: F876 programming questions' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/microchip/devprogs.htm?key=programming
Search entire site for: 'F876 programming questions'.

Exact match. Not showing close matches.
PICList Thread
'[PIC]: F876 programming questions'
2001\01\29@172731 by Mike Mansheim

flavicon
face
>I activate VCC then a few 10's of millisecs later raise MCLR from ground
>to ~13V. That's all you need to do. The 72 osc clocks will relate to the
>reset feature in the chip. The OSC1 pin should be tied low (or high),
>and not left floating, before and during the programming process to stop
>any clock pulses incrementing the program counter.

Tony, thanks for the response.
When I do this "in-circuit", when I activate Vcc, MCLR will also rise to
Vcc.  Then I am raising MCLR from Vcc instead of from ground.  Also, since
the chip in installed on a target board, the OSC pins are hooked up, so I
would think the chip would actually "run" for the period of time between
activating Vcc and raising MCLR.  This is the mode of operation I'm trying
to get a handle on.
Thanks again for the help.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2001\01\29@173351 by Tony Nixon

flavicon
picon face
Mike Mansheim wrote:
>
> >I activate VCC then a few 10's of millisecs later raise MCLR from ground
> >to ~13V. That's all you need to do. The 72 osc clocks will relate to the
> >reset feature in the chip. The OSC1 pin should be tied low (or high),
> >and not left floating, before and during the programming process to stop
> >any clock pulses incrementing the program counter.
>
> Tony, thanks for the response.
> When I do this "in-circuit", when I activate Vcc, MCLR will also rise to
> Vcc.  Then I am raising MCLR from Vcc instead of from ground.  Also, since
> the chip in installed on a target board, the OSC pins are hooked up, so I
> would think the chip would actually "run" for the period of time between
> activating Vcc and raising MCLR.  This is the mode of operation I'm trying
> to get a handle on.
> Thanks again for the help.

This is why I included an open collector output for ICSP on my new
programmer design. This goes low during programming and can be used to
pull the OSC1 or RB3 pin low.

--
Best regards

Tony

mICro's
http://www.picnpoke.com
spam_OUTsalesTakeThisOuTspampicnpoke.com

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2001\01\29@211259 by Bob Ammerman

picon face
My understanding of the programming algorithm is that you do _not_ have to
hold off the oscillator by forcing it low, if you meet the spec for Vpp/MCLR
transition from Vss to Vpp (ie: 72 osc clocks).

The chip will ignore the osc completely if Vpp/MCLR is valid at Vpp within
those 72 clocks.

For example, the ICD will work perfectly to program an F876 with only Vcc,
Vss, MCLR/Vpp, RB6 and RB7 connected.

There is no need to do anything to the clock, or in my experience, RB3/LVP -
although some have claimed problems with the latter.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)


{Original Message removed}

2001\01\29@213852 by Roman Black

flavicon
face
Mike Mansheim wrote:

> When I do this "in-circuit", when I activate Vcc, MCLR will also rise to
> Vcc.  Then I am raising MCLR from Vcc instead of from ground.  Also, since
> the chip in installed on a target board, the OSC pins are hooked up, so I
> would think the chip would actually "run" for the period of time between
> activating Vcc and raising MCLR.  This is the mode of operation I'm trying
> to get a handle on.
> Thanks again for the help.


According to the Microchip ICSP app note, this is a
big no-no.

The PIC should be held in reset (MCLR low) while
it is powered up, then MCLR should go from 0v to
13v as quickly as possible to avoid the possibility
that a proper clock cycle will occur and the
program counter is incrememented. That would cause
the new program to be written at the wrong address,
ie start+x (x is how many clock cycles occured).
Microchip are quite specific about this, and they
also state that capacitances on circuits attached
to MCLR should be kept very low. I use no caps
on MCLR, instead I tie it to 5v with a 68k resistor.
-Roman

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


More... (looser matching)
- Last day of these posts
- In 2001 , 2002 only
- Today
- New search...