Setting DTR high, RTS low using Linux bash?

Question

I have a serial device that has no flow control, but is powered from the RS232 port by holding the RTS high and DTR low

I was hoping to read from this device using a simple bash script, but can't find any way to set the handshaking lines, using stty or otherwise, to allow for the above configuration.

Any ideas if this is possible?

Answer 1

I don't have an answer about setting RTS without touching DTR, because I don't have any DTR pin on my dongle; but, trying to set RTS was already very tricky un pure shell.

You may need to play with stty crtscts and clocal flags.

I have published a detailed answer here: https://forums.gentoo.org/viewtopic-p-8132756.html#8132756

Here is the short version:

#!/bin/bash
MySerialPort="/dev/ttyUSB0"
MyLatency="2"
echo "#include <fcntl.h>
#include <sys/ioctl.h>
main()
{ int fd; fd = open(\"${MySerialPort}\",O_RDWR | O_NOCTTY );
int RTS_flag; RTS_flag = TIOCM_RTS;
ioctl(fd,TIOCMBIS,&RTS_flag);
sleep (${MyLatency});
ioctl(fd,TIOCMBIC,&RTS_flag);
close(fd); } " | tcc -run -

Note that sending data on TX will probably mess RTS; see the Gentoo forum for details.

Answer 2

socat controls DTR when hucpcl=1

(Atmel EDBG USB Serial needs DTR high)

sleep 1; while true; do echo -en "\x01\x02"; sleep 0.1; done | socat -T1 -t1 - /dev/ttyUSB0,hupcl=1,raw,b1000000,cs8,echo=0

man socat - may be find more solutions for your serial problem.