I'm using 2-wire RS485 for communication between a network of 8051 based devices, in a single master/multiple slave half-duplex configuration.

I'll be sending async data over the line, so my research indicates that I should use fail-safe biasing so that when no device is driving the line all receivers will see mark idle and not be confused.

This leads me to think that maybe I don't ever need to drive the line into the mark state, but I could just disable the line driver and let the fail-safe biasing take control. Using this scheme, I would have the 485 transmit data input tied to ground, and feed the transmit enable with an inverted version of the desired transmit data stream.

Driving RS485 this way will remove the need to have an IO for enabling/disabling the transmit driver, and removes any issues with timing on that control line (like ensuring that all data bits are fully out before disabling the driver).

What are the disadvantages with this scheme? I would think that there must be some, or else everyone would do RS485 this way...