My Friends Merry Christmas and Happy New year. Would you give me an example about how to connect SN75179 chip or equivalent to realize RS485 communication? I can realize communication between two AT89S52 directly using RXD and TXD, but when I inserted a couple SN75179 chips (every one connected with 120 0hm resistor) they died. What are the possible reasons? Thank you.
TO PROTECT THE DRIVER I PUT ALSO 2 RESISTOR (10 OHM) IN SERIES TO SIGNAL A AND B NEAR CONNECTOR. ALSO 2 SUPPRESSOR (TRANSIL AND/OR VARISTORS 30V D=7) FROM A AND B TO METAL CASE PROTECT THE BOARD AND MICROPROCESSOR FROM EMC BURST. IS IMPORTANT ALSO A 3° WIRE WITH 100 OHM TO CONNECT ALL BOARDS GROUND IN THE CASE OF GALVANIC ISOLATION. THE COMMON MODE VOLTAGE AT A AND B CAN DAMAGE DRIVER (SEE DATA SHEET). YOU CAN EVALUATE ALSO MAX485 FROM MAXIM THAT IS MORE PROTECTED.
DON'T SHOUT!
TO PROTECT THE DRIVER I PUT ALSO 2 RESISTOR (10 OHM) IN SERIES TO SIGNAL A AND B NEAR CONNECTOR Please get a new keyboard where the caps lock is not stuck. The two 10 ohm resistors will, indeed, protect the chip but create havoc with the terminations. a much better idea is to use a chip that can handle the load such as The LT1785/LT1791 from linear technology http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1007,C1017,P1713 which can, in adiition to surges, withstand a constant + or - 60 volts on the A and B in/outputs. Our "wonderful" costomers like to put 28 Volts on the signal lines and these chips can handle it!. One word of caution: If you want this to be totally survivable, you need to up the wattage of your terminating resistors. Erik