Read from external serial port

i have a automate that store error code in her memory and offer a serial port to communicate with it
my need is to use arduino to send msg to automate via serial port and receive the error stored in her memory to display it on a liquidCrystal but i dont know how to do this.

We have a francophone section ici if it would help you.

Do you have a datasheet of your 'automate'? If so, please provide a link.

First question is what the 'automate' uses? RS232 serial or TTL serial. For the RS232 serial, you will need a level converter like a MAX232 between the Arduino and the 'automate'.

Second would be which settings your 'automate' requires? 9600/8N1? or ...

Do you already have an Arduino? Which one?