Meilhaus Electronic ME-90 Series, Electronic Manual, Page: 54 / 120

transfer is done in a differential way. A voltage difference of more
than +200
mV at the receiver input is defined as high-level and a
voltage difference of less than -200 mV as low-level. The RS-485
standard is an extension of the RS-422 standard and allows up to
32 transmitters/receivers, which can be in half-duplex or full-duplex
mode. Every transmitter/receiver must have a unique address.
Note that the transfer rate decreases with increasing cable
length. See the following Picture to calculate the max. transfer
rate (max. 921,6 kBd, depending on board version) in dependency of
cable length (max 1200
m).
Note: Keep the signal levels (see specifications on page 101).
3.7.2.1 RS-422
The RS-422 standard provides serial data transfer up to 1200 m
by two twisted pair wires for optimum noise immunity. Beside the
ME-9000/9100 resp. ME-90 PC/104-Plus maximum one more
transmitter and up to 10 receivers are allowed. Usage of
termination resistors R
T
(50…500
Ω
, depending on characteristic
resistance) is recommended.