Mentioned why to have bias resistors

Author: majenkotech

docs/RS485.md

@@ -11,13 +11,13 @@ A basic transceiver circuit based around the popular MAX485 (or MAX3485 for 3.3V
 
 ![MAX485 transceiver circuit](max485.png)
 
-The "Bias Resistors" should only be provided at one location within the RS-485 bus, and should be in the order of 560Ω.
+The "Bias Resistors" should only be provided at one location within the RS-485 bus, and should be in the order of 560Ω. The purpose of these is to hold the signals at a stead idle state when all the units on the bus are in receive mode.
 
 The "Termination Resistor" should be present at both ends of the bus, but not in the middle. This should be as close to the end of the cable as possible and should match the characteristic impedance of the cable as closely as possible. For typical twisted pair cable this would be somewhere around 100Ω-120Ω.
 
 Connecting the nodes together into a bus is done like this:
 
-RS-485 Bus
+![RS-485 Bus](max485bus.png)
 
 The cable should be shielded twisted pair, with the shield connected to ground at each node via a resistor Rg (typically 100Ω). Note how the bias resistors Rb are only present at one end, and the middle nodes lack the terminating resistor Rt. The distance between the bus cable and node 2 should be kept as short as possible - ideally the bus cable would enter one side of node 2 and exit the other side to keep the distance to an absolute bare minimum.