Rs485comCircuit

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=== Circuit description of IRS422HVrevB.pdf ===
Download http://www.rs485.com/downloadfiles/IRS422HVrevB.pdf to follow the circuit description below
=== Circuit description of IRS422HVrevB.pdf ===
 * Tx+ and R+ means non-inverting. 
 * The RS232 chip has a permanent high on pin.9. 
 * Data is transmitted by pulling pin9 low.
 * The schmidt trigger inverts ans squares it creating a low over R1 and diode. 
 * With a RxD pulse Rs232pin9 goes low and the green led on R1 indicates this.
 * The next smidth trigger inverts the signal, creating a low. 
 * The optical coupler 6N137 gets a low on the cathode of the diode. 
 * Current flows through R8 pulsing the ANDgate. 
 * The AND gate sinks current and R11 is pulled low.
 * Schmidt trigger goes high sourcing current through R15 flashing the red diode.
 * The RxD pulse is immediatly on pin5 of the RS422.
 * R13,R12 and C5 forms a low pass filter and propagation delay network.
 * This enables the RxD signal to stabilise on pin5 before pin4 of the RS422 is activated. 
 * The timing diagram of the AMD489AN indicates that xxxxuS after a stable signal is on pin9 must it be clocked through. 
 * The TwistedPair connects to pin9,10 transmitting the RxD pulse over 4000ft to pin9,10 of the other RS422 ic.
 * 620ohm pulldown and pullup biasing resistors are placed on all lines to enable a 200mv biasing voltage. 
 * TX- and TX+ are protected with two fuses. 
=== Simulate RS485 with RS422 ===
 * Use one TwistedPair
 * J3 and B are connected for RS485 mode. J3 and A are for Full-duplex RS422 mode
 * The RS422 chip can be used in either full-duplex mode RS422 or half-duplex. 
 * A RS422 chip can be used to simulate RS485 communication.
 * Connect J10, J11 for RS485 mode.
 * The Tx-(inverting) line of board1 connects to the Rx- line of board1 via J11
 * Tx+(inverting) of board1 connects to its Rx+ line via J10
 * Board2 Rx+ connects via TwistedPair to Board1 Rx+
 * Board2 Tx+ connects to Board1 Tx+
 * With board in receive mode there is a permanent LOW on RE-422
 * RxD goes low RE gets a high putting it in Tri-state.
 * The DE pin gets a high and transmits the RxD pulse. 
 * Only one board can transmit at a time. 
 * All the other boards on the multi-drop network are in receive mode. 
=== Full duplex RS422 mode ===
 * Use two TwistedPair or 4-wires.
 * Via J3 RS422 active low RE has a permanent low to enable permanent recepetion. (get datasheet)
 * Tx+ board1 connects via TwistedPair to Rx+ board2. And Tx- to Rx-
=== Links ===
 * RS485 chipset are extremely cheap around $1.50