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Old 01-12-2005, 07:28 AM   #1
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Registered: Jan 2005
Posts: 16

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Serial port transfer

Hi all,
i'm writting a programm to transfer data via serial port. I'd like to test it on my computer first, so i connected serial ports and wrote a simple program just to check the connection. I write one character into ttyS0 and want to read it from ttyS1. Writing works OK (numb_send = 1) but there is some problem with reading (numb_rec = -1). I think, port settings are OK.

ttyS0: Line 0, UART: 16550A, Port: 0x03f8, IRQ: 4
Baud_base: 115200, close_delay: 50, divisor: 0, closing_wait: 3000

ttyS1: Line 1, UART: 16550A, Port: 0x02f8, IRQ: 3
Baud_base: 115200, close_delay: 50, divisor: 0, closing_wait: 3000

Shall I set anything else? Thank you for your advise.

#include <stdio.h>
#include <sys/signal.h>
#include <sys/types.h>

int main(void) {

int fd1, fd2;
int numb_send,numb_rec;
char c;
char buf[5];

fd1 = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NONBLOCK);
if (fd1 < 0) {

fd2 = open("/dev/ttyS1", O_RDWR | O_NOCTTY | O_NONBLOCK);
if (fd2 < 0) {

numb_send = write(fd1,&c,1);
numb_rec = read(fd2,buf,sizeof(buf));
printf("sent: %d\n received: %d\n",numb_send,numb_rec);
Old 01-12-2005, 02:13 PM   #2
Registered: Aug 2003
Location: Akron, OH
Distribution: Fedora Core 3
Posts: 185

Rep: Reputation: 30
does that require using a null-modem cable?


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