RS485 bus communication circuit based on transformer

Abstract

The invention relates to a RS485 bus communication circuit based on a transformer. The circuit uses CN1 and CN2 as network port connectors; a RS485 signal passes through third and sixth pins of a network port; a signal on a bus is connected to first and second pins of a primary terminal of the transformer through a network cable; the signal is transmitted to a secondary side through the transformer; a third pin of the transformer is connected to a first pin of a common-mode inductor and a second pin of D1; a fourth pin of transformer is connected to a second pin of the common-mode inductor anda first pin of the D1; a third pin of the D1 is connected to GND; a secondary side of the transformer applies capacitance C1 and C2 to the GND; the signal is filtered by the common-mode inductor, andreaches seventh and eighth pins of U1; an eighteenth pin of the U1 is connected to Vcc; capacitance C3 is applied to the ground; second and fifth pins of the U1 are connected to the GND; and first, third and fourth pins of the U1 are connected to an MCU (Microprogrammed Control Unit). Through adoption of the RS485 bus communication circuit, the anti-interference ability is improved, and the technical problem of complex design of a bus type RS485 isolator is well solved. The RS485 bus communication circuit has the characteristics of compatibility, simplicity, practicability, easiness in understanding and control, long service life and low design cost.

Description

technical field [0001] The invention relates to a transformer-based RS485 bus communication circuit. Background technique [0002] RS485 is a low-speed serial communication interface, which is widely used in industrial fields. It supports point-to-multipoint half-duplex data communication, and the sending and receiving signals occupy the same bus (twisted pair) in time division. In order to avoid bus conflicts, when the level is 0, the A and B lines are actually driven by the output terminals of the chip, and UB-UA=5 V; when the level is 1 or when the bus is empty, the output terminals of the chip show high resistance, and the A and B lines are changed to External resistors bias and make UA slightly larger than UB. There is usually a large ground potential difference in remote data connections, and when the resulting common-mode interference is too large or in a strong interference environment, it will often cause bit errors or hardware damage. At present, in order to impr...

AI Technical Summary

Problems solved by technology

[0005] The invention adopts the pulse transformer isolation, which not only improves the anti-interference ability, but also better solves the complicated technical problem of the design of the bus-type RS485 isolator, and can isolate the signal without providing an isolated power supply separately, without considering the data flow direction, and in a limited The baud rate is self-adaptive within the range, and it is compatible, simple and practical, easy to understand and control, etc. At the same time, the service life of the transformer is longer than other products, and the design cost is low

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