Freeport Mode; Creating User-Defined Protocols With Freeport Mode - Siemens SIMATIC S7 System Manual

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Freeport mode

Introduction

Freeport mode allows your program to control the communication port of the

S7-200 SMART CPU. You can use Freeport mode to implement user-defined

communication protocols to communicate with many types of intelligent devices. Freeport

mode supports both ASCII and binary protocols.

Using Freeport mode

To enable Freeport mode, you use special memory bytes SMB30 (for the Integrated RS485

port (Port 0)) and, if your CPU model supports it, SMB130 (for the CM01 Signal Board (SB)

port (Port 1)). Your program uses the following to control the operation of the communication

● Transmit instruction (XMT) and the transmit interrupt:

The Transmit instruction allows the S7-200 SMART CPU to transmit up to 255 characters

from the COM port. The transmit interrupt notifies your program in the CPU when the

transmission has been completed.

● Receive character interrupt:

The receive character interrupt notifies the user program that a character has been

received on the COM port. Your program can then act on that character, based on the

protocol being implemented.

● Receive instruction (RCV):

The Receive instruction receives the entire message from the COM port and then

generates an interrupt for your program when the message has been completely

received. You use the SM memory of the CPU to configure the Receive instruction for

starting and stopping the receiving of messages, based on defined conditions. The

Receive instruction allows your program to start or stop a message based on specific

characters or time intervals. Most protocols can be implemented with the Receive

instruction, instead of using the more cumbersome receive-character interrupt method.

S7-200 SMART

System Manual, V2.3, 07/2017, A5E03822230-AF

Communication

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Simatic s7-200 smart