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'[PIC]:Regarding MCLR(pin 1) of pic16f877'
2001\02\11@180316 by o-8859-1?q?SZE=20KEAT=20CHEE?=

picon face
Hello everyone

   Sorry if this is a too simple
question.
   I would like to know :
(1)It is is okay for to connect this
  mention pin 1 to Vdd(5V) for all
  the project?Or should I connect it
  to a reset IC.Howver , I have a
  reset IC(monolithic ic pst600)
   with me,but I dont know the value
   the resistor and the capasitor that
   I should put.

    Vdd(5V)<--------------
              |           |
              |           |
            --------      |
            | reset |  resistor( ? )
            |  ic   |     |
            |       |     ------->pin 1 of
            ---------     |        pic16f877
               |          |
               |          =capasitor(? )
               |          |
    Gnd  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^


Please correct me if my interfacing is wrong.

Chee Sze  Keat


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2001\02\11@183918 by Byron A Jeff

face picon face
>
> Hello everyone
>
>     Sorry if this is a too simple
> question.

There are no simple questions... Ask away.

>     I would like to know :
> (1)It is is okay for to connect this
>    mention pin 1 to Vdd(5V) for all
>    the project?

The PIC has a power on reset circuit internally. As long as +5 meets the
required risetime. Here's the quote from Section 12.4 from the datasheet:

A Power-on Reset pulse is generated on-chip when
VDD rise is detected (in the range of 1.2V - 1.7V). To
take advantage of the POR, tie the MCLR pin directly
(or through a resistor) to VDD. This will eliminate exter-
nal RC components usually needed to create a Power-
on Reset. A maximum rise time for VDD is specified.
See Electrical Specifications for details.
When the device starts normal operation (exits the
reset condition), device operating parameters (voltage,
frequency, temperature,...) must be met to ensure oper-
ation. If these conditions are not met, the device must
be held in reset until the operating conditions are met.
Brown-out Reset may be used to meet the start-up con-
ditions. For additional information, refer to Application
Note, AN007, "Power-up Trouble Shooting",
(DS00007).

The minimum listed risetime is 50 mV/ms. So the power supply must rise
to 5V within 100 ms.

>    Or should I connect it
>    to a reset IC.

Only if the power supply does not meet the risetime requirement.

>Howver , I have a
>    reset IC(monolithic ic pst600)
>     with me,but I dont know the value
>     the resistor and the capasitor that
>     I should put.

You need to make sure that the power is stable when the part is out of
reset. But again unless you have an extremely slow rising power supply
it's pretty much unecessary.

BAJ

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2001\02\11@201910 by o-8859-1?q?SZE=20KEAT=20CHEE?=

picon face
Hi Byron

   Thanks a lot for your advice
and explaination.I got it.
   I think I connect it to vdd(5V).

  Thanks again.

Chee Sze Keat

--- Byron A Jeff <spam_OUTbyronTakeThisOuTspamCC.GATECH.EDU> wrote: > >
{Quote hidden}

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