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'[PIC] Internal clock'
2005\12\15@074229 by o, Edson Jose

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Hi all!

Is the internal clock of 16F88 and 16F628A sufficiently accurate for
"RELIABLE" Asynchronous Serial Communication?

I did some tests and seem it works fine for speeds up 19200 bps.

Is it possible that I have problems with temperature or power supply
variations?

Thanks,
Edson.






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2005\12\15@083252 by Wouter van Ooijen

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> Is the internal clock of 16F88 and 16F628A sufficiently accurate for
> "RELIABLE" Asynchronous Serial Communication?

I would not trust it, but some people on this list would. Problems might
occur due to supply voltage and temperature variations. If you can
guarantee 20 C and 5.0 V it might work reliably, for some value of
reliably. But a resonator is cheap ....

> I did some tests and seem it works fine for speeds up 19200 bps.

Contrary to popular belief the speed does not matter.

Wouter van Ooijen

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Van Ooijen Technische Informatica: http://www.voti.nl
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2005\12\15@170822 by Mike Hord

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> Is the internal clock of 16F88 and 16F628A sufficiently accurate for
> "RELIABLE" Asynchronous Serial Communication?

What is the clock's accuracy in the temperature range of the
application?  I think I've heard the number .5% bandied about-
total error in the async serial link should not exceed .5% (+/-)
for reliable communication.  Note that this figure includes both
stability and accuracy of the internal clock as well as any
error in the generated frequency of the serial data.

> I did some tests and seem it works fine for speeds up 19200 bps.

As Wouter said, speed doesn't matter- it's accuracy of the serial
clock you're worried about.  Of course, speed DOES matter, in a
way, because the baud rate generator will do some baud rates
better than others.  For example, the 18F2320 can do 1.2, 2.4, or
9.6 kbaud at .16% accuracy, but try and do 57.6 kbaud, and your
error value bumps up to 3.55%.

> Is it possible that I have problems with temperature or power supply
> variations?

Of course.  The datasheet will give you some idea of what those
variations will be, across your desired temperature range or the
range of acceptable power supply voltages.

Mike H.

2005\12\16@072210 by Vasile Surducan

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On 12/15/05, Martignago, Edson Jose <spam_OUTEdson-Jose.MartignagoTakeThisOuTspaminvista.com> wrote:
> Hi all!
>
> Is the internal clock of 16F88 and 16F628A sufficiently accurate for
> "RELIABLE" Asynchronous Serial Communication?
>
> I did some tests and seem it works fine for speeds up 19200 bps.

115200, software communications OK between 10C to 60C, only with pics
with oscal.

Vasile


{Quote hidden}

> -

2005\12\16@080225 by ike, K8LH (sent by Nabble.com)

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I've had good results using INTOSC for RS-232 communications with devices operating at stable room temperatures...

You might also consider using some of the newer PIC devices with 8-MHz INTOSC and 16-bit SPBRG capability (the 20 pin16F690, 28 pin 18F2420-2520-2620, 40 pin cousins 18F4420-4520-4620)...  The 16-bit SPBRG modes offer very precise control and adjustment of baud rate...  For example, here's a screen shot of the SPBRG Calculator spreadsheet displaying 16-bit SPBRG solutions...

Happy Holidays...  Regards, Mike



Here's a link to the SPBRG Calculator spreadsheet on Forum.Microchip;

forum.microchip.com/upfiles/22956/Mk26167.jpg
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2005\12\19@062349 by o, Edson Jose

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I'd like to thank every body for the info about the subject.

Edson.

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