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USB to RS485 converters

They allow you to control Modbus devices via one of the COM ports. This section shows two types of converters: a converter that transmits only data, and another one that transmits data and voltage through the USB port. They are not Master devices, they just forward data and electricity.

From USB to Modbus data


Figure 1 - USB to RS485 converter

This USB to RS485 converter simply converts data lines such as signal D- and signal D+ to RS485 and does not transmit any voltage. The Table 1 found below summarizes these. After you have wired the converter and the serial device together, you can connect it to the PC. Note that the converter supports only none parity! Due to it does not transmit voltage, the devices connected with this USB to RS485 converter need an external power supply.

USB side/input Description RS485 side/output
VCC +5V none
D- Data- B
D+ Data+ A
GND Ground none
Table 1 - USB to Modbus data

From USB to RS485 with voltage


Figure 2 - USB to RS485 converter plus 5V

This USB to RS485 converter transmits the data lines to RS485 and also transmits the voltage and ground line. Ideal for devices that exactly need 5V came from the PC via USB cable. The Table 2 below summarize the inputs and outputs. To attach it to your computer, you need an USB 2.0 - mini USB cable. It does not support parity even!

USB side/input Description RS485 side/output
VCC +5V +5V
D- Data- B
D+ Data+ A
GND Ground GND
Table 2 - USB to Modbus data plus 5V

From USB to RS485 with parity even and odd


Figure 3 - USB to RS485 converter with parity even and odd

This USB to RS485 converter is a cleverer one. It also transmits the serial data lines and the voltage, but it is already supports the parity even and odd! The Figure 3 above shows how to wire and and the following table summaries the input and output of the converter.

USB side/input Description RS485 side/output
VCC +5V RX+
D- Data- D-
D+ Data+ D+
GND Ground RX- / GND
Table 3 - USB to RS485 with parity even and odd

Buy the converters

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