Keywords: Modbus FreeModbus STM32F103C8T6 CubeMX
With only serial communication, the hardware design is relatively simple. Kong Binghuo (WeChat public account: Kong Binghuo) believes that it can be roughly divided into three parts: MCU, power supply, and 485, as shown in Figure 1, Figure 2 and Figure 3.
figure 1
figure 2
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The microcontroller uses STM32F103C8T6. From the knowledge of Kong Binghuo (WeChat public account: Kong Binghuo), this microcontroller is one of the more commonly used models. UART1 has been used for ISP download and serial printing. UART2 is used for RS485 communication. The whole board uses DC5V power supply, which is converted to 3.3V through AMIS1117 to power the microcontroller. RS485 uses isolation design. The isolation power supply uses IB0505S-W75R3. The isolation voltage is 1500VDC, 485. Signal conversion and isolation use ADM2483BRWZ. Add an external watchdog SP706SEN to the single-chip part, and at the same time have the power supply monitoring function, the single-chip microcomputer will be reset when the single-chip power supply is lower than 2.93V. The MCU has a SWD interface for program debugging. Since the load range of IB0505S-W75R3 is 10%-100%, in order to ensure the stability of the power supply, Kong Binghuo (WeChat public account: Kong Binghuo) adds a dead load of R8 to the output. The ADM2483BRWZ uses a magnetic isolation design inside. Although the cost is higher, the circuit design is simple and can also save PCB area.
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