Special driving method of RS485 circuit in dual opto-isolator periphery application

Abstract

The invention discloses a special driving method of an RS485 circuit in dual opto-isolator periphery application, which comprises the steps as follows: when the signal of an RE / DE port is '1', the RS485 circuit is in a normal driver mode; when the signal of the RE / DE port is changed from '1' into '0', the RS485 circuit is in a special driving mode, at the moment, the RS485 circuit generates a driving signal of '1' or '0', if the RE / DE port always retains the signal of '0', a counter continues counting until the counter is full, the RS485 circuit quits the special driving mode and returns to the normal operation mode, and a normal communication function is continuously realized; if the signal of the RE / DE port recovers '1', the RS485 immediately recovers the normal driver mode, and normal driving is kept going. The method can realize driving ability of three opto isolators, has a periphery application mode of dual opto-isolator, is suitable for a new national power grid standard, saves opto isolators, pull-up resistors and pull-down resistors, and lowers cost.

Description

technical field [0001] The invention relates to a driving method of a circuit, in particular to a special driving method of an RS485 circuit in the peripheral application of two optocouplers. Background technique [0002] At present, RS485 circuits are widely used in ammeter circuits and other related fields. The existing RS485 circuit generally has two peripheral application methods: one is as attached figure 1 As shown, the peripheral application mode of two optocouplers is used: the RE and DE ports of the RS485 circuit are connected together and two optocouplers are connected to the RO port respectively, the DI port is grounded, the control signal is given by the MCU, and the A and B ports are added to the pull-up and pull-down resistance. In this application mode of two optocouplers, the RS485 circuit driving "0" signal is provided by its own drive. When the RS485 circuit is required to provide a "1" signal, the resistance of the A and B ports to the power supply and t...

AI Technical Summary

Problems solved by technology

In this application mode of three optocouplers, when the RS485 interface circuit is required to provide "0" and "1" signals, the DI port controls the A and B ports to output "1" and "0" signals, and the driving ability is strong , but it needs to consume one more control port of the MCU, and use one more optocoupler to connect to the DI port, the cost is high

[0004] According to the requirements of the new standard issued by the State Grid in January 2013, the A and B ports of each meter must realize the function of automatically judging the polarity, and it is impossible to add pull-up and pull-down resistors to enhance the driving ability

In order to meet the requirement of driving ability, each electric meter factory can only adopt the scheme of three optocouplers, which increases the cost

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