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08-25-2005, 02:22 PM
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#1
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LQ Newbie
Registered: Apr 2004
Distribution: Slackware & Gentoo & Ubuntu
Posts: 22
Rep:
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Serial Port : How do I raise DTR
How do i raise DTR for a serial port application?
I think I am confused about using and's, or's .
The Posix Serial Port How-To shows how to lower DTR :
#include <unisdt.h>
#include <termios.h>
int fd
int status;
ioctl(fd, TIOCMGET,&status );
status &= ~TIOCM_DTR;
ioctl( fd, TIOCMSET, &status );
I woud really appreciate it if anyone could help with this.
thanks in advance,
Tom
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08-25-2005, 05:08 PM
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#2
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Senior Member
Registered: Aug 2002
Location: Groningen, The Netherlands
Distribution: Debian
Posts: 2,536
Rep: 
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Code:
/* Parameter "level" should be zero or non-zero for
* setting to low or high resp.
* Assumes fd is a global open filedescriptor
* variable to a serial device.
*/
int setDTR(unsigned short level)
{
int status;
if (ioctl(fd, TIOCMGET, &status) == -1) {
perror("setDTR()");
return 0;
}
if (level) {
status |= TIOCM_DTR;
} else {
status &= ~TIOCM_DTR;
}
if (ioctl(fd, TIOCMSET, &status) == -1) {
perror("setDTR");
return 0;
}
return 1;
}
Last edited by Hko; 08-25-2005 at 05:12 PM.
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08-25-2005, 06:54 PM
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#3
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LQ Newbie
Registered: Apr 2004
Distribution: Slackware & Gentoo & Ubuntu
Posts: 22
Original Poster
Rep:
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Thank You!!
So it looks like I can assume to lower a value (x) always use something like :
x &= ~y
and to raise a value (x) use :
x |= Y
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08-26-2005, 05:17 AM
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#4
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Senior Member
Registered: Aug 2002
Location: Groningen, The Netherlands
Distribution: Debian
Posts: 2,536
Rep: 
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Quote:
Originally posted by ttumelty
So it looks like I can assume to lower a value (x) always use something like :
x &= ~y
and to raise a value (x) use :
x |= Y
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Well yes, sort of. Keep in mind though that this is about the bits, zeroes and ones. If y == 7, there will be 3 bits set to '1' (high). So x |= y will set 3 bits in 'x' to high. The included header that #defines TIOCM_DTR is a bit-mask, with 1 bit set to '1'.
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