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Andypugh, Thanks for reply!

I didn't use mesa board. I think about ehtercat + rs232 , this is more simple for me (ethercat modules avaible from stock, but mesa is not available). But of course best way to use onboard rs232 to sending and receiving data.

About realtime -This is not critical , because speed is 19200, so i dont need realtime.

I will read links more detailed this evening.
And may be there are some another way if no needed realtime.

Does your system have a Mesa card? If it does then you could look at using a Mesa UART.

Otherwise it ought to be possible to use the onboard serial port, but for some reason I haven't seen anyone do that through HAL in realtime.

In theory you ought to be able to do it with inb and outb commands:
stackoverflow.com/questions/47048726/bau...-outb-commands-linux
(note that the advice there is "don't" but they are not considering realtime limitations)

There is an existing hal component that uses the serial port status lines for GPIO
github.com/LinuxCNC/linuxcnc/blob/master...drivers/serport.comp
which it might be possible to tweak. But the fact that nobody seems to makes me wonder if it is impossible for some reason?