DS8921AT: Pull-up, pull-down and terminator resistors in line.

Hi Nikita,

In RS-422, a termination resistor is typically placed between the differential data lines at the end of the cable opposite the transmitter. The resistance value should match the characteristic impedance of the cabling used, which is typically something like 100 Ohms or 120 Ohms. This resistor makes sure that the signals propagating down the cable do not see an impedance mismatch once they reach the cable end. This helps to prevent reflections from distorting the signal waveform. The termination is not required in all applications, though - if the cable distances are short and the data rates (switching speed as well as transition times are low) then it is possible for the link to operate without termination. A 2-m cable would likely fall into this category, although you should evaluate it using an oscilloscope monitoring the differential line to be sure that signal quality is maintained.

You can find more details on RS-422 termination here: www.ti.com/.../slla070d.pdf.

Best regards,
Max