This project is a RS232 to RS485 interface module
This circuit has been designed around popular MAX232 and MAX485 interface IC.This project provides a simple and easy solution to connect your computer to a RS485 Network in either Receiver or Transmitter mode.
An Onboard 9 pin female ?D? connects this PCB to the Serial Port cable (not supplied with the Kit). Connector J1 and J2 provide the MAX232 IC input/output (IO) and Connector CN1 provide MAX485 IO. An optional Power Supply section can provide regulated 5V DC to the circuit and can be included to power by bridging Jumper J4. LED D2 provides visual indication of power on this board and Diode D1 prevents against reverse polarity connection of power supply at J3. This circuit can also work on 5V supply from the host interface which can be provide through J1 in which case you need to remove Jumper Link @ J4. Connector J2 provide extra connection of the other set of level shifter with in the MAX232 IC.
RS485 cable is to be connected at Connector CN2 and are impedance matched with Components R3, R1 and R4.
Terminal marked ?A? on CN1 is the Receive / Transmit control Pin for the RS485 flow control. Pulling this pin to Gnd will enable the Receiver on the RS485 and Pulling it High (connecting it to Vcc) will enable it to work in the transmit mode.
To connect the MAX232 IC to the MAX485
1. Connect Pin marked C on connector J1 to Pin marked DI on connector CN1
2. Connect Pin marked B on connector J1 to Pin marked RO on connector CN1
Connector J1 connects to the Host for power supply and serial In/Out signals.
A ? Provides data from the Computer to the Host (RXD)
B ? Provides data to be sent to the Computer from the Host (TXD)
Supply input 5-12 VDC Max
Source: Electronics Lab