Unleash the true potential of your data network with SN65HVD31 and STM32F091RC

RS485 3 Click is based on the SN65HVD31, a tristate differential line driver and differential input line receiver, from Texas Instruments. This click is intended to be used as a physical layer device, often referred to as PHY, providing physical interfacing of the MCU TTL level UART lines with the RS422/485 bus. It is well suited for transmitting smaller blocks of data over long distances, using two differential pairs, one for TX and other for RX line, allowing for full-duplex asynchronous communication. The SN65HVD31DR transceiver consists of a separate driver and receiver sections, which are always active upon powering the device. Driver section is used to drive the RS422/485 bus with the signal received on the UART RX line labeled as D on the IC, while the receiver section returns data from the bus back to the MCU via the UART TX line, labeled as R on the IC in the schematics. RS422/485 standard only specifies electrical characteristics of the transmitter and the receiver. It does not specify or recommend any communications protocol, only the physical layer. The top layer communication protocol of choice can be used, such as the MODBUS or DMX protocols. Therefore RS485 3 click offers UART RX and TX pins, routed to the appropriate mikroBUS™ TX and RX UART pins. These pins are used by the MCU to send data to the RS485, in a form determined by the used protocol. Please note that RS485 3 click supports only 3.3V MCUs and it is not

intended to be connected or controlled via the 5V MCU without a proper level shifting circuitry. The SN65HVD31DR IC allows communication with data rates up to 5 Mbps. However, the maximal transfer speed is determined by the bus length: longer bus lines will result in less transfer speed. The RS422/RS485 bus needs to be terminated with the resistor on both ends, which is equal to the characteristic impedance of the used cable, in order to prevent line reflections. The RS485 standard prescribes using a twisted pair cable as the data bus. Twisted pair cable tends to cancel common-mode noise and causes cancellation of the magnetic fields generated by the current flowing through each wire, thereby reducing the effective inductance of the pair. The RS-485 standard specifies that a compliant driver must be able to drive 32 unit loads (UL), where 1 unit load represents a load impedance of approximately 12 kΩ. Since the SN65HVD31 device is 1/8 UL, up to 256 such receivers can be supported by a single driver. When used as the master, the driver section of the RS485 3 click is always active. The same is true for the slave receivers on this same signal pair. In the case when slaves need to communicate back to the master, they are using another pair and the slave device drivers have to be intermittently enabled and disabled so that only one driver on a slave is enabled at a time. Since the SN65HVD31 device does not contain RE and

DE (Receiver Enable and Driver Enable) pins, slave driver cannot be disabled, resulting with bus contention, where the differential voltage can increase so that the resulting current can damage the IC. In that case, the driver current protection is activated, limiting this current to 250mA. Differential inputs contain internal Schmitt trigger circuits, preventing uncertain states of the pins. This ensures that the outputs are always in a defined state, also providing noise immunity. To further improve the signal integrity, RS485 3 click is equipped with two transient voltage suppression diodes (TVS diodes) used to protect the circuit from transients that can occur on the RS422/485 bus. There are two 2-pole screw terminals on board (RX+, Rx-, Tx+, Tx-) for connecting RS422/485 bus twisted pair cables, along with two screw terminals (GND) for common ground connection. The cables should be connected as close as possible to the termination resistors, preventing signal reflections in the parts of the signal cable that is not terminated by the resistor, so-called stubs. MikroElektronika provides a library that contains functions compatible with the MikroElektronika compilers, which can be used for working with the RS485 3 Click. The library also contains an example application, which demonstrates their use. This example application can be used as a reference for custom designs.

Nucleo-64 with STM32F091RC MCU offers a cost-effective and adaptable platform for developers to explore new ideas and prototype their designs. This board harnesses the versatility of the STM32 microcontroller, enabling users to select the optimal balance of performance and power consumption for their projects. It accommodates the STM32 microcontroller in the LQFP64 package and includes essential components such as a user LED, which doubles as an ARDUINO® signal, alongside user and reset push-buttons, and a 32.768kHz crystal oscillator for precise timing operations. Designed with expansion and flexibility in mind, the Nucleo-64 board features an ARDUINO® Uno V3 expansion connector and ST morpho extension pin

headers, granting complete access to the STM32's I/Os for comprehensive project integration. Power supply options are adaptable, supporting ST-LINK USB VBUS or external power sources, ensuring adaptability in various development environments. The board also has an on-board ST-LINK debugger/programmer with USB re-enumeration capability, simplifying the programming and debugging process. Moreover, the board is designed to simplify advanced development with its external SMPS for efficient Vcore logic supply, support for USB Device full speed or USB SNK/UFP full speed, and built-in cryptographic features, enhancing both the power efficiency and security of projects. Additional connectivity is

provided through dedicated connectors for external SMPS experimentation, a USB connector for the ST-LINK, and a MIPI® debug connector, expanding the possibilities for hardware interfacing and experimentation. Developers will find extensive support through comprehensive free software libraries and examples, courtesy of the STM32Cube MCU Package. This, combined with compatibility with a wide array of Integrated Development Environments (IDEs), including IAR Embedded Workbench®, MDK-ARM, and STM32CubeIDE, ensures a smooth and efficient development experience, allowing users to fully leverage the capabilities of the Nucleo-64 board in their projects.