16F628 USART by internal OSC

Yu · Guest

Hi all.
I wrote RS232C code using internal 4MHz osc.
Some 16F628 works good, but some does not work.
Is internal osc suited for USART use ?

Does anyone have the same experience ?

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

I've used it with no problems. However you can improve the timings by getting the internal clock out to a pin, measureing it and then using that figure in your delay statment.

Will

davidpk · Joined: 29 Apr 2004 Posts: 13 Location: Opelika, AL

I am using an 18F452 at 40MHz. I was sending out data at 115,200 and things were working fine until I tried to send out a long string. I reduced the bps to 57,600 and it is working fine.

RS-232 can put up with quite a bit of error in the timing but when you are sending out long strings the errors add up and it looses synch. (looses async?) If you send the data in shorter bursts then you can get away with more slop in your timing.