RS422/485 4 wire and RS485 2 wire with one IC

[asadi.siyavash]

Hi,
I am really confused I saw some equipment that work with 2 wire and 4 wire RS485. they used same wire so they used one IC for converting. as you see in the picture

but as I understood from MAX3490 just can support four wire. how I can used it or some IC like this in both condition 2 wire and 4 wire without need any change in the PCB.
please help me,
all the best
Siyavash

 

[D.A.(Tony)Stewart]

• 2 wire must be half duplex with MUX switch and master slave control.
• 4 wire may be full duplex and no Mux needed.

 

[asadi.siyavash]

i know but how can implement with something like MAX3490

 

[FvM]

You can't connect MAX3490 for half-duplex (two-wire RS-485) operation because it misses a tristatable driver respectively a TX-enable function. You can use e.g. MAX489 and your design must be able to generate the required direction information.

 

[asadi.siyavash]

could you give me a shematic diagram of what you said? as you said user should manually select 2 wire or 4 wire communication? or not without any changes like above image it can work with 2 wire and 4 wire.
any help would be greatly appreciated.

 

[FvM]

I expect the product is using something like MAX1381, RS-422/485 transceiver with logic selectable half-/full-duplex mode.