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Circuit description of IRS422HVrevB.pdf Edit

Download http://www.rs485.com/downloadfiles/IRS422HVrevB.pdf to follow the circuit description below

Circuit description of IRS422HVrevB.pdf Edit

* 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 Edit

* 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 Edit

* 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 Edit

* RS485 chipset are extremely cheap around $1.50

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