rs422 uses 4 wires am i correct to assume that 2oof the wires are for sending data and the other 2 are for recieving data between master and slave units
It is quite simple actually.
RS422 is for full duplex data transmission. 2 wires are used to transmit data. 2 wires are used to recieve data.
The databits HI or LO are detected as a voltage difference between the two wires. This is the big difference to RS232 where the voltage is measured to a common ground wire.