As with any product family, RS-485 has its own lexicon, with the key terms listed here. Slew rate limited denotes drivers with purposely slow output transitions to minimize EMI, and reflections in unterminated or poorly terminated networks. Typical families have two levels of slew rate limiting targeted at data rates in the 120 to 250 kbps range and another for 500 kbps to 1 Mbps rates. Devices targeted for data rates greater than 1 Mbps are usually not slew rate limited. To minimize potential electromagnetic problems, slew rate limited drivers should be utilized whenever data rates allow for it. Failsafe receivers refer to their ability to maintain a defined state even when common input faults occur. Most RS-485 protocols use a high logic level as the idle state, so it is desirable for a receiver output to remain high unless valid data is being received. Extraneous high to low output transitions – or worse yet chattering – are interpreted as message start bits, and result in wasted processor bandwidth from servicing phantom messages. Receivers that maintain a high level only when the inputs are floating – as when a connector disconnects from a bus – are known as failsafe open devices. Failsafe shorted receivers maintain the high output level with a differential input voltage of 0V. Receivers with both failsafe open and shorted are called full failsafe or true failsafe devices. Thermal shutdown indicates that the IC senses when the die temperature exceeds a safe level – usually around 150°C – and automatically disables the transmitter outputs. Receiver outputs are usually left enabled because the excessive heating is almost always caused by bus contention or faults on the driver side. When the die temperature cools, the transmitter is re-enabled; the disable and re-enable cycle continues until the fault is cleared. Half duplex refers to RS-485 ICs with the corresponding receiver input and driver output sharing the same package pin. ICs of this type are ideal for applications requiring bidirectional communication over a single twisted pair. Full duplex ICs have four separate pins for the receiver inputs and the transmitter outputs, and are intended for applications using two pairs for bidirectional communication. RS-422 devices are always full duplex types.