Parts - MAX485 Serial line transceivers

Specifications

• MAX485 module - RS485 to TTL RS232 transceiver board
• Half-duplex operation (single twisted pair)
• Max data rate: 2.5MBps
• Max devices per bus: 32
• Quiescent current: 300µA

Pinout description

• A, B - the twisted pair comms line
• Vcc, Gnd - Power 4.75V ≤ Vcc ≤ 5.25V
• RO - Receiver output - ttl level serial RX
• R̅E̅ - Receiver Output Enable - enabled when low
• DI - Driver Input - ttl level serial TX
• DE - Driver Output Enable - enabled when high

RS-485 uses a single twisted pair of wires to connect upto 32 devices together in a bus fashion, each end should be "terminated" with a 120ohm resistor across the pair. The system is half-duplex, so only one unit should be in transmit mode at a time, all others should be in receive mode, or off. RS-485 defines only the physical interface, it is up to the end user application to supply any protocol that is required.

Resources

•  Datasheet
• Wikipedia Definition
• Guidelines for proper wiring