I need some help communicating with a serial port device. I have the serial port set to "auto" IRQ in the BIOS. The device (a Temperature controller) has the following Data protocol:

Tx Start bit:1
Tx Data Bit:1
Tx stop bit:2
Rx Start bit:1
RX Data bits:8
RX Stop Bits >=1

The device last had a UNIX interface.

when I open cutecom using root, I get this message:

~# cutecom 
QInotifyFileSystemWatcherEngine::addPaths: inotify_add_watch failed: No such file or directory
QFileSystemWatcher: failed to add paths: /root/.config/ibus/bus
Bus::open: Can not get ibus-daemon's address. 
IBusInputContext::createInputContext: no connection to ibus-daemon

I am not clear on how to locate the device in /dev dmesg shows a tty serial device:

$ dmesg | grep tty
[    0.000000] console [tty0] enabled
[    0.708459] 00:07: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A

so then I cd'd into /sys/class/tty/ttyS0 and cat dev to get the major and minor number

#cat /sys/class/tty/ttyS0/dev

I also checked tty0

#cat /sys/class/tty/tty0/dev

So then I looked for those items in /dev and found their user friendly names:

# ll -R /dev | grep "4, *0"
crw-------   1 root root      254,   0 Mar 24 12:43 rtc0
crw--w----   1 root tty         4,   0 Mar 24 13:14 tty0
# ll -R /dev | grep "4, *64"
crw-rw----   1 root dialout     4,  64 Mar 24 13:04 ttyS0

no mater what I send, I get nothing back from the cutecom console: cutecom running from root

So, Now i am confused. It would seem like the device is present, but when cutecom makes the connection, and I enter commands, I get nothing back in the console, and the device doesn’t seem to respond. I think I must be doing something wrong. How can I verify that this serial device is connected to my computer? what can i do to troubleshoot this connection?


I found the solution. When the VT sensor is connected to the NMR that it gives feed back to, a null modem is used. When I went to connect the VT to my computer, I also used a null modem. After trying every combination, of settings, I tried getting rid of the null modem, and using a regular serial cable.

At that point, I was able to send commands, and get data back.

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