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Truth tables

The STR485 is a half-duplex differential driver/receiver compliant to the RS485 communication standard (ISO-IEC

8482). This product is perfectly adapted for low voltage application running with a low power supplies VL,

generally set to 1.8 V and VCC set to 3.3 V.

These voltages confer a low power consumption to the product.

SLR is the data rate selection, this pin could be let floating but it is not recommended; in that case the high speed

rate is automatically selected.

The SLR pin must be connected to the ground to provide a high speed communication up to 20 Mbps.

When this pin is connected to VL power supply, the data rate is limited to 250 kbps more adapted for very long

distance data transmission.

Figure 4. Block diagram

The product is perfectly adapted to run with 256 devices on the same bus thanks to the internal output resistance

that is over 96 kΩ up to 105 °C; this resistance follows the RS485 condition that requests a minimum of 12 kΩ for

32 unit loads (UL).

The STR485 has internal protection against ESD that protect each device driver output and receiver input. The

limits have been tested up ±4 kV electrostatic discharge (HBM) and ± 8 kV contact discharge and ± 16 kV air

discharge shocks without latch-up.

Another external protections can be used to increase the communication robustness against different perturbation

that can be seen on the application.

The power supplies must be well-decoupled by a minimal capacitor of 0.1 µF as closed as possible to the device

power supply input. Moreover, the capacitor should be higher on the application with a minimum of 1 µF around

the device.

The device operating range is set from VL = 1.65 V to 3.6 V and for Vcc = 3.0 V to 3.6 V. In any case VCC must

be higher or equal than VL.

The applications should respect this voltage constraints to let the application communication device run to the

best conditions.

STR485

Truth tables

DS12713 - Rev 1

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