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Serial Port Timing Issues With DS89C450


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Rouslan Nabioullin

Fri Jul 10 2009, 02:46PM

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I am trying to get this serial port output sample program to work with the hardware I'm using (2400 baud, 12MHz xtal):

CODE:

#include <stdio.h>

#include <reg420.h>

// Initialize serial port 0 to 14400 baud (16.384MHz crystal)

serialInit()

{

TMOD = 0x21; // Timer 1: 8-bit autoreload from TH1

TH1 = 220; // 14400 baud rate

CKMOD = 0x38; // Use system clock for timer inputs

T2CON = 0x00; // Serial 0 runs off timer 1 overflow

TCON = 0x50; // Enable timers 0 and 1

SCON0 = 0x50; // Enable serial port 0

SBUF0 = ' ';

}

void main()

{

serialInit(); // Initialize serial port 0

printf("\rHello from the Keil C51 compiler\r");

while (1) {

printf("test1\r");

printf("test2\r");

}

}

Any ideas on what values I should modify the parameters to?

[ Edited Fri Jul 10 2009, 02:48PM ]

Ajay Bhargav

Sat Jul 11 2009, 11:09AM

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you need to calculate timer reload value (TH1) for 12Mhz, 2400 baud.

check uart chapter of datasheet to find out how the clock works for this controller. if you face any problem do post here.. will help.

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Rouslan Nabioullin

Sun Jul 12 2009, 08:49AM

Registered Member #20175

Joined: Fri Jul 10 2009, 02:40PM

Posts: 2
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I found the UART timing characteristics on pages 9-10: http://datasheets.maxim-ic.com/en/ds/DS89C430-DS89C450.pdf
But I'm still unsure what values I should set the parameters to - I simply need a starting point so I could learn about the 8051 and UART timing once it actually works (i.e. prints actual text). Thanks in advance.

[ Edited Sun Jul 12 2009, 08:51AM ]

Ajay Bhargav

Mon Jul 13 2009, 01:17PM

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as you are using a ultra high speed controller from Dallas, there are many things to take care when using uart.. like mode of timer clock, CPU clock multiplier etc..

you need to go through page 42 of datasheet (link you posted) or download a detailed datasheet of this controller.

else keep everything default and use it like a generic 8051 controller where timer value is calculated as:

TH1 = 256-((2^SMOD)/32 * OscFrequency/(12*Baud))

so you get your reload value for timer.

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