Magic Crystals

[andybarrett1]

Hi Henrik

Thank you.... I am using Hserin/out at 9k6.

As I say.... Would like to get my head round using the more appropriate Xtal frequencies for Serial coms... As need to interface a GPS soon. so a lot more data = more errors

BR
Andy

[pedja089]

What is problem with 4MHz crystal?
It has only 0.16% error for 9600 baud rate.
Internal counters are reset on every start bit, so there is no accumulation of error if you have lot of data.
I always use 4 or 8 MHz crystal with modems and Bluetooth modules, so far there was no problem in communication due to baud rate error.

[andybarrett1]

Works Fine with 4Megs Xtal But :-

Surely no error is better than 0.16% error... Plus I learn more by experimentation and help !!

HW guy in a SW world !!

[HenrikOlsson]

Agreed, but with this comment "everything times 0.9216, a PAUSE 100 becomes PAUSE 922.", don't you mean PAUSE 100 becomes PAUSE 92?

Yes, of course, I meant to write PAUSE 1000 but a zero must have fallen off at the end there, sorry about that and thank you for pointing it out. Of course, I'm not allowed to edit my own post, stupid rules I still don't understand.

Although 0% error is indeed better than 0.16% error, 0.16% error is, in this case, really not much. personally I wouldn't worry about it.

If the chip you're using has the EUSART then going to 16MHz will allow you to get -0.08%, 20MHz -0.03% and 24MHz will put you right on the number - all these clock frequencies are supported by PBP.

/Henrik.

[andybarrett1]

Hi Henrik

I drop 0's all the time or add them... don't worry :-)

The chip I am using is the 16f688 so will go to 20Mhz no problem....I will just do that I think. keeps the pauses etc easier to understand.

Thank you for help everyone

Appreciated !