I have choosen an active high decoder and an active low decoder:
74HCT154 (active low) -> connected to RE (bar)
74HCT4514 (active high) -> connected to DE
... the idea here is that by default, the RE(bar) will be set to high and the DE will be set to low. Now, whenever the correct rs485 is choosen to be written into, its DE will be set to high. Similarly, the RE(bar) will be set to low whenever something needs to be read from the RS485. I am hoping that this is going to work (it seems to be simple... atleast for me :-))
1. Since I am connecting as many as 10 (or may be even 16) maxium's max485s to the arduino's RX and TX pins, should I worry about noise?
Moreover, at somepoint in the future, this board that I am making will be placed near a power supply something similar to this:http://www.mouser.com/ProductDetail/Mean-Well/SP-240-12/?qs=sGAEpiMZZMu0oxGuRuNKH0QVy%252bJkdvy3TE%2fqNU8V00M%3d
As a matter of fact, this power supply will be connected to the arduino.
2. Does it make sense to attach two 100K pull down resistors to both TX and RX to prevent noise?
3. Does the power supply induce any electrical noise into the Rx and TX pins?
4. What is the best way to insulate RX and TX pins?... I am open to the idea of having 4-6 layers within the board and dedicating two layers to RX and TX.
Any advice is highly appreciated... thanks.