The SN65HVD21M offers performance exceeding typical RS-485 devices. In addition to meeting all requirements of the TIA/EIA-485-A standard, the HVD2x family operates over an extended range of common-mode voltage, and has features such as high ESD protection, wide receiver hysteresis, and failsafe operation. This family of devices is ideally suited for long-cable networks, and other applications where the environment is too harsh for ordinary transceivers.
The SN65HVD21M is designed for bidirectional data transmission on multipoint twisted-pair cables. Example applications are digital motor controllers, remote sensors and terminals, industrial process control, security stations, and environmental control systems.
The SN65HVD21M combines a 3-state differential driver and a differential receiver, which operates from a single 5-V power supply. The driver differential outputs and the receiver differential inputs are connected internally to form a differential bus port that offers minimum loading to the bus. This port features an extended common-mode voltage range making the device suitable for multipoint applications over long cable runs.
The SN65HVD21M allows up to 256 connected nodes at moderate data rates (up to 5 Mbps). The driver output slew rate is controlled to provide reliable switching with shaped transitions which reduce high-frequency noise emissions.
The receiver also includes a failsafe circuit that provides a high-level output within 250 µs after loss of the input signal. The most common causes of signal loss are disconnected cables, shorted lines, or the absence of any active transmitters on the bus. This feature prevents noise from being received as valid data under these fault conditions. This feature may also be used for Wired-Or bus signaling.
The SN65HVD21M is characterized for operation over the temperature range of -55°C to 125°C.
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