Special Hardware Requirements:
One connection cable, 9-pin
If more than two PLCs are used (more than one slave), you will need a Siemens network bus connector.
In this example, three SIMATIC S7-200 CPUs are connected. Each one is a CPU 214. Station 0, called the master, is linked to stations 1 and 2, called the slaves. The master station sends four bytes of output data to each station in turn. As a result, each station responds with four bytes of input data. The Freeport communication mode is used for the data transmission.
Two memory buffers are reserved: one for remote inputs and one for remote outputs. The output data that is to be transmitted is captured by moving a double word value from the output buffer to the Transmit buffer. After transmitting, the master station receives the response of the slave stations and stores the data in the Receive buffer.
This program includes several timed interrupt routines. Each timed interrupt routine is called by one of the following two interrupt events: interrupt event 10 and event 11. For example, in this program, interrupt event 10 calls timed interrupt routine INT0 and timed interrupt routine INT1. At one point in the program, interrupt event 11 calls INT0.
The time interval for a timed interrupt routine that is called by event number 10 is specified in special memory byte SMB34. The time interval for the timed interrupt that is called by event number 11 is specified in special memory byte SMB35. In both cases, the time interval is fixed in increments of 1 ms. The smallest value permitted for the time interval is 5 ms. The largest value permitted for the time interval is 255 ms.
In this program, the time interval specified in SMB34 is 5 ms. The time interval that is specified in SMB35 is 20 ms.
It is also possible to use the Network Read (NETR) and Network Write (NETW) instructions to link a CPU 214 to other S7-200 CPUs in the Point-to-Point Interface (PPI) mode. In the PPI mode, it is possible to connect TD 200 units and operator panels (OPs) to the network and still link the stations together.
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