Siemens SIMATIC S7-1200 System Manual page 1101

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Message end conditions

You also configure how the communication interface recognizes the end of a message. You

can configure multiple message end conditions. If any one of the configured conditions

occurs, the message ends.

For example, you could specify an end condition with an end of message timeout of 300

milliseconds, an inter-character timeout of 40 bit times, and a maximum length of 50 bytes.

The message will end if the message takes longer than 300 milliseconds to receive, or if the

gap between any two characters exceeds 40 bit times, or if 50 bytes are received.

Recognize message end by

message timeout

Recognize message end by

response timeout

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK

The message end occurs when the configured amount of time to wait for the message end

has expired. The message timeout period begins when a start condition has been satisfied.

The default is 200 ms and the range is 0 to 65535 ms.

Received characters

Start Message condition satisfied: message timer starts

Message timer expires and terminates the message

The message end occurs when the configured amount of time to wait for a response ex-

pires before a valid start sequence is received. The response timeout period begins when a

transmission ends and the CM or CB begins the receive operation. The default response

timeout is 200 ms and the range is 0 to 65535 ms. If a character is not received within the

response time period, RCVTIME, then an error is returned to the corresponding RCV_PTP

instruction. The response timeout does not define a specific end condition. It only specifies

that a character must be successfully received within the specified time. You must config-

ure another end condition to indicate the actual end of a message.

Transmitted characters

Received characters

First character must be successfully received by this time.

Communication processor and Modbus TCP

13.3 Point-to-point (PtP) communication