I am going to connect several micro-controllers together using half-duplex RS485, but there is no absolute master or slave, each micro must be able to communicate others and this will cause problems if both of them want to send data at the same time (one makes A high and B low and the other makes A Low and B high, that will cause short circuit) so I am thinking of adding pull-up and pull-down resistors to the lines and send data by changing state of TxEn pin instead of TxDt pin of RS485 ICs.
Here is my problem:
- Pull-up, pull-down and EOL resistors form a voltage divider on the RS485 data lines, does it make data communication problems?
- What happens if I ignore EOL resistors and just apply pull-ups and pull-downs at both ends?
- Is there any relation between maximum cable length and resistors value?
- Does using higher data voltage increases the data transmission reliability? If yes, is there any 12V RS485 ICs? (12V is the absolute maximum ratings of MAX485 and LTC1685, what about safety factor?)
BTW, if I have two 100ohm EOL resistors and 5V data voltage it means that communication consumes 100mA, that is too high for a device that consumes only 5mA, and it makes the devices to have a big voltage regulator and capacitors in comparison with other components!
^^^ A diagram I found in LTC1685 datasheet ^^^