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'[PIC]: PIC16C628 ER mode'
2002\12\05@150339 by Dave King

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face
Just wondering if anyone has used or can clarify how to use the ER
Oscillator mode.

I know the 628 has the internal 4mhz osc which I will probably use but I'm
curious what
exactly the ER OSC is. The spec sheet has a one paragraph description on
what it is,
and suggests between a 38K and 1M resistor but it never says what the
result is.
It does say it for applications that are not time sensitive but that is a
just little too vague
 as to the speed it produces.

Anyone have any insights?

Dave

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2002\12\05@152646 by Wouter van Ooijen

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What is it that you don't understand? The ER is like the internal RC
oscillator, except that the frequency is determined by an external
resistor, and that this resistor carries only DC (important: stray
capacitance has no effect, no radiation etc). The R->F relation is
missing from the uChip documentation, but some piclister has measured it
and it can be fund at http://www.voti.nl/fader. This page describes an
application that makes good use of the ER mode.

Wouter van Ooijen

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2002\12\05@153507 by Spehro Pefhany

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At 12:01 PM 12/5/02 -0800, you wrote:
>Just wondering if anyone has used or can clarify how to use the ER
>Oscillator mode.
>
>I know the 628 has the internal 4mhz osc which I will probably use but I'm
>curious what exactly the ER OSC is. The spec sheet has a one paragraph
>description on
>what it is, and suggests between a 38K and 1M resistor but it never says
>what the
>result is.

Yes, that has been noted. You just connect a resistor to ground from RA7.

>It does say it for applications that are not time sensitive but that is a
>just little too vague as to the speed it produces.
>
>Anyone have any insights?

Jinx has made measurements, and posted them earlier this year. Here they
are again below. There are no guarantees, if you really need the time
to be within better than +/-30-50% of nominal you might look to some other
way, at least until Microchip does some characterization.


(credit to Jinx for these measurements)
------------------------------------------------
These are practical measurements for 16F628-04

R Clkout * 4
2k7 9.40MHz
3k3 9.35
4k7 9.23
10k 8.44
22k 5.65
39k 3.50
100k 1.52
220k 0.75 MHz
470k 0.393
1M 0.192
1M5 0.124
2M2 85,600 Hz
5M6 36,400
12M 16,400


Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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2002\12\05@155317 by Dave King

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face
>Jinx has made measurements, and posted them earlier this year. Here they
>are again below. There are no guarantees, if you really need the time
>to be within better than +/-30-50% of nominal you might look to some other
>way, at least until Microchip does some characterization.
>
>Spehro Pefhany

I found another set of measurements with radically different osc speeds.
I see what they meant by non-sensitive timing applications.  I think I will
definitely stick with the internal oscillator.

Thanks

Dave

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