Innovative Idea: Communicating Between PLCs Without RS485 or Ethernet for Multi-Data Transmission ~ [With Tutorial]

Last night, unable to sleep, I had a sudden idea: how can PLC1 communicate with PLC2 without RS485 or Ethernet if we need to transmit multiple data?

Thus, I came up with the following hypothesis and experiments:

Idea:

If PLC1 oscillates at a certain frequency AND outputs data 0/1, isn’t that a way to output data?

How does the next PLC receive it? How does data 0.1 start?

1: How does the lower-level machine determine that the upper-level machine is sending data?

Is this feasible? PLC1 outputs a fixed ON pulse of 200MS, then the lower-level PLC2 can determine that a signal has arrived if the input exceeds 200MS;

Instead of talking so much, why not try it out practically?

The PLC used is the easy301 from Inovance, the lowest-end model, with Y0 input connected to X0 output, physically wired;

1. Set the X terminal filter to 2ms (the minimum);

2. Write a program with two timers oscillating back and forth. After testing, the delay from Y0 output to X0 input is 1.9-2.2MS;

Alright, it seems feasible, let’s write the program:

1. Calculate the timer time based on the input frequency.

//1hz = changes once every 1s, 500MS on and 500MS off

vd_通讯频率:=REAL_TO_DINT(500.0/ir_通讯频率);

2. Write the logic, let’s do it step by step;

Test, sending 4 words, 64 bits;

FB function block, 4 int arrays, internal 64-bit array, assign values.

Use a table to illustrate;

First step: then keep the key ON for 200MS, signaling the lower PLC to prepare to send data;

Second step: the critical step, two timers oscillate AND 64-bit array = Q point output;

Above, keep 200MS ON, then follow with the data

The first line is to start sending, the first line is the data waveform, below is the DONE signal, then write the receiving parsing program, as follows:

Then the effect is as follows:

1. If the receiving end is set to 200MS, it may not receive, I changed it to 199.

2. The timer oscillation frequency cannot be too fast, otherwise it will be abnormal and data will be lost;

There was no optimization, just a test to see if it could be used. Theoretically, PLC can communicate with multiple slave PLCs, referencing Modbus-RTU, and CRC can be used to check if the data is OK.

Although the PLC input terminal has filtering, the speed is slow, but it works. One I/O terminal can transmit so much data, which I feel can be used in places where timing requirements are not high.

Source: China Industrial Control Network

Author:bnnyygy

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