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Achieve baud rate 921600

Started by Soon Heng August 31, 2004
Hi,

How is it possible to achieve fast serial baud rate of
115200,230400,460800,921600? I was trying to communicate with the PC at
these rates. Using a 20MHz clock frequency is not possible due to deviation
errors? What actually affects the desired baud rate, and how do I achieve
this common PC standards??

Thks
Heng


"Soon Heng" <soonheng@ps-electronic.com> wrote in message
news:ch3l3e$g3v$1@mawar.singnet.com.sg...
> Hi, > > How is it possible to achieve fast serial baud rate of > 115200,230400,460800,921600? I was trying to communicate with the PC at > these rates. Using a 20MHz clock frequency is not possible due to
deviation
> errors? What actually affects the desired baud rate, and how do I achieve > this common PC standards??
Use a 18.432 MHz clock. Meindert
Meindert Sprang wrote:
> > "Soon Heng" <soonheng@ps-electronic.com> wrote in message > news:ch3l3e$g3v$1@mawar.singnet.com.sg...
>> How is it possible to achieve fast serial baud rate of >> 115200,230400,460800,921600? I was trying to communicate with the PC at >> these rates. Using a 20MHz clock frequency is not possible due to >> deviation errors? What actually affects the desired baud rate, and how >> do I achieve this common PC standards?? > > Use a 18.432 MHz clock.
That is 20x the max bit rate. If the UART wants a 8x clock, 14.7456 MHz (16x) would work better. Thad
"Thad Smith" <thadsmith@acm.org> skrev i meddelandet
news:4135E4E6.56A0993C@acm.org...
> Meindert Sprang wrote: > > > > "Soon Heng" <soonheng@ps-electronic.com> wrote in message > > news:ch3l3e$g3v$1@mawar.singnet.com.sg... > > >> How is it possible to achieve fast serial baud rate of > >> 115200,230400,460800,921600? I was trying to communicate with the PC at > >> these rates. Using a 20MHz clock frequency is not possible due to > >> deviation errors? What actually affects the desired baud rate, and how > >> do I achieve this common PC standards?? > > > > Use a 18.432 MHz clock. > > That is 20x the max bit rate. If the UART wants a 8x clock, 14.7456 MHz > (16x) would work better. > > Thad
The normal PC uses a 24 MHz clock and a by 13 prescaler. 24 MHz / 13 / 16 (oversampling) => ~115,200 BAUD. Some newer generation PCs support running without a prescaler. This was introduced in the NSC PC87108 (IIRC) and is probably in later SuperI/Os. but I do not think it is supported by any Operating Systems. Note that this does not allow you to communicate with that speed. You can communicate with the PC at that speed, if you put a USB to Serial adapter in between your unit and the PC. The AT76C711/2 runs this comfortable using PLL technologies. -- Best Regards Ulf at atmel dot com These comments are intended to be my own opinion and they may, or may not be shared by my employer, Atmel Sweden.
On Wed, 1 Sep 2004 18:14:33 +0200, "Ulf Samuelsson"
<ulf@NOSPAMatmel.com> wrote:

> >"Thad Smith" <thadsmith@acm.org> skrev i meddelandet >news:4135E4E6.56A0993C@acm.org... >> Meindert Sprang wrote: >> > >> > "Soon Heng" <soonheng@ps-electronic.com> wrote in message >> > news:ch3l3e$g3v$1@mawar.singnet.com.sg... >> >> >> How is it possible to achieve fast serial baud rate of >> >> 115200,230400,460800,921600? I was trying to communicate with the PC at >> >> these rates. Using a 20MHz clock frequency is not possible due to >> >> deviation errors? What actually affects the desired baud rate, and how >> >> do I achieve this common PC standards?? >> > >> > Use a 18.432 MHz clock. >> >> That is 20x the max bit rate. If the UART wants a 8x clock, 14.7456 MHz >> (16x) would work better. >> >> Thad > >The normal PC uses a 24 MHz clock and a by 13 prescaler. >24 MHz / 13 / 16 (oversampling) => ~115,200 BAUD. > >Some newer generation PCs support running without a prescaler. >This was introduced in the NSC PC87108 (IIRC) >and is probably in later SuperI/Os. >but I do not think it is supported by any Operating Systems. > >Note that this does not allow you to communicate with that speed. >You can communicate with the PC at that speed, if you put >a USB to Serial adapter in between your unit and the PC. >The AT76C711/2 runs this comfortable using PLL technologies.
I use these most often with uC's for higher speeds (8052 derivitives): 22,118,400 = 115200 baud PCON.7 = 1 TH = 0xFF 24,576,000 = 128000 baud PCON.7 = 1 TH = 0xFF If the processor your using can handle it then: 49,152,000 = 256000 baud PCON.7 = 1 TH = 0xFF 44,236,800 = 230400 baud PCON.7 = 1 TH = 0xFF These crystal frequencies are commonly available. I never bothered to calculate higher baud rates because of OS support issues and stability problems. USB is the way to go for improved speed. 18,432,000 is a good all-round frequency (18,432,000 = 300, 600, 1200, 2400, 4800, 9600, 19200) but I prefer 22,118,400, you can easily get quite a few of the common baud rates from it (22,118,400 = 300, 600, 1200, 1800, 2400, 4800, 7200, 9600, 14400, 19200, 38400, 57600, 115200). ----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =---