Max485 Circuit with Hex invertor circuit

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prabhukaran3

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Dear All,
Currently I am doing reverse engineering of a product.. Almost everything is done..
Problem is in communication section(RS-485) they used hex invert-or (74HC04).. Previously I am having lot of experience with max485 circuits. RE(2nd pin) and DE pins should be connected to same . I/O/ for receiving/transmitter we do high or low before data transfer starts..

In this hardware they have connected RE pin to output of one hex invert-or same for DE too. input pins off hex is connected two separate I/O lines... Little bit in confuse.. Our device is not communicating in Rs-485...
I need to know what is the use of hex invert-or here?.. Please explain
 

It does not sounds good...Taking Multiple IO lines and connecting it to a single input doesn't make sense. Simply remove one connection from the IO line and try to communicate. The Hex inverter is nothing acts as a buffer with the inverted case. So you need to drive 1 from IO pin to work as receiver and drive 0 from IO pin to work as driver.
 

It isn't essential RE and DE are joined and driven from a single point, if it was, the manufacturer would only use one pin for the job. The RE pin is a tri-state control for the RO pin so it can share a connection with other devices on a bus.

Brian.
 

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