PIC UART Rates

[AtomSoft]

Hello all i wanted to ask something that may be simple...

I wanted to send data at 4800bps i usually just get the info from the data sheet but this isnt a common speed i guess heh...

So i need to do the calculations. Now the issue is :

1. Im not sure if im right...
2. I have 2 speeds 1 micro is 20mhz and the other is 40mhz so im doing it for both..

The PIC in question is a 18F2525..
From Datasheet:

For a device with FOSC of 16 MHz, desired baud rate of 9600, Asynchronous mode, 8-bit BRG:
Desired Baud Rate = FOSC/(64 ([SPBRGH:SPBRG] + 1))
Solving for SPBRGH:SPBRG:
X = ((FOSC/Desired Baud Rate)/64) – 1
= ((16000000/9600)/64) – 1
= [25.042] = 25
Calculated Baud Rate = 16000000/(64 (25 + 1))
= 9615
Error = (Calculated Baud Rate – Desired Baud Rate)/Desired Baud Rate
= (9615 – 9600)/9600 = 0.16%

20Mhz:
20000000/4800 = 4166.666666666667
4166.666666666667 / 64 = 65.10416666666667
65.10416666666667 - 1 = 64.10416666666667
64.10416666666667 = 64
((20000000/4800)/64)-1 = 64

20000000/(64(64+1)) = 4807.692307692308
(4807.692307692308 - 4800)/4800 = 0.0016025641025642 %

Correct?

40Mhz:
40000000/4800 = 8333.333333333333
8333.333333333333 / 64 = 130.2083333333333
130.2083333333333 - 1 = 129.2083333333333
129.2083333333333 = 129
((40000000/4800)/64)-1 = 129

40000000/(64(129+1)) = 4807.692307692308
(4807.692307692308 - 4800)/4800 = 0.0016025641025642 %

Correct?

Exact same speed.... Would these values work ? I find it a pain in the butt to test 2 PICs communicating.... so i want to ask before i go nuts if i get some bad results heh i know it wasnt this...

EDIT:
I remember there being a calculator of some sort or a speed sheet formula... i dont know how to use those really to make my own but would love if someone can repost them heh

 

[ericgibbs]

Hi atom, look at this.

 

[AtomSoft]

YAY!!!! thanks... just tested it and works fine!!! my calculations was spot on ... i did something right!! i feel great now heh... Thanks again Eric...

 

[Sceadwian]

Find the value for 9600 and divide by two, much simpler math =)

 

[Mike - K8LH]

Jason,

I wrote a stand-alone SPBRG Calculator several years ago that supports 16-bit and legacy 8-bit SPBRG solutions (on Forum.Microchip). The code generator portion of the program is not completed.

Revised SPBRG Calculator (spreadsheet and stand-alone program)

Mike

**broken link removed**

 

[AtomSoft]

YES!! this is the one i used to use too!...

I used the other for timers i think heh

More direct link heh:
https://www.microchip.com/forums/fb.aspx?m=179347