Pic Baud rate

[JeffreyPeter]

Which crystal MHz is best suited for generating baud rate for PIC ?
I want it to generate 2400/9600 ...connecting with PC.
Thanks in advance..

 

[geko]

In general for such low bit rates the internal HF oscillator will work fine in asynchronous applications assuming the PIC you intend to use has that feature.

If you're using a PIC with an internal UART the bit rate generator module can be set to generate the bit rates you specify quite accurately so you don't really need to use a crystal that divides perfectly.

From a 4Mhz crystal or internal clock your can get:
2403bps (+0.13% off 2400)
9615bps ( +0.16% off 9600)

With asynchronous comms the receiver syncs to the start bit of each frame so the error doesn't accumulate over frames.

- if this doesn't help tell us what PIC you are using and more details on what you are trying to acheive.

 

[Ian Rogers]

I use 11.0592MHz for precision but a standard 20MHz will give excellent results at 9600 baud.. If you look at the tables in the data sheet most crystals will get a reasonable baud error...

 

[dr pepper]

I have a temp/humidity/rain sensor on the garage roof, it talks back to this pc at 9k6, the chip is a 16f628a and it uses a max232c to generate the correct volatges for rs232, the chip uses its on board osc, everything works fine.
I can post you the init subroutine for the uart if you really want.

 

[Mr RB]

You don't need much in the way of precision in the baudrate. A single byte will function fine with a baud error as high as 5%, provided you re-sync on each new byte by using 1.5 or 2 stop bits (a tiny extra pause between bytes of 0.5 to 1 bit pause length).

For lowish baudrates like 9600 and below any PIC xtal should get you within 1% or so of perfect.

 

[AtomSoft]

14.7456MHz will give you just about all baud rates you could ever want

 

[Mike - K8LH]

If anyone is interested, there's an SPBRG Calculator spreadsheet in this old Forum.Microchip thread; Revised SPBRG Calc

**broken link removed**

 

[AtomSoft]

yep love your program

View attachment 68695

 

[be80be]

I read a appnote about using serial for debugging can't remember what chip it was code was in C but at this low rate it didn't matter
if your off 5% it still works fine. So im with RB here

PIC xtal should get you within 1% or so of perfect.