Siemens SIMATIC S7-1200 System Manual page 1102

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Communication processor and Modbus TCP

13.3 Point-to-point (PtP) communication

Recognize message end by

inter-character gap

Recognize message end by

receiving a fixed number of

Recognize message end by

Read message length from

Recognize message end

with a character

Recognize message end

with a character sequence

The message end occurs when the maximum configured timeout between any two consec-

utive characters of a message has expired. The default value for the inter-character gap is

12 bit times and the maximum number is 65535 bit times, up to a maximum of eight sec-

Received characters

Restarts the intercharacter timer

The intercharacter timer expires and terminates the message.

The message end occurs when the specified number of characters has been received. The

valid range for the fixed length is 1 to 4096.

Note that for the S7-1200, this end condition is only valid for V4.0 CPUs or higher.

The message end occurs when the configured maximum number of characters has been

received. The valid range for maximum length is 1 to 1023.

This condition can be used to prevent a message buffer overrun error. When this end con-

dition is combined with timeout end conditions and the timeout condition occurs, any valid

received characters are provided even if the maximum length is not reached. This allows

support for varying length protocols when only the maximum length is known.

The message itself specifies the length of the message. The message end occurs when a

message of the specified length has been received. The method for specifying and inter-

preting the message length is described below.

The message end occurs when a specified character is received.

The message end occurs when a specified character sequence is received. You can speci-

fy a sequence of up to five characters. For each character position, you specify either a

specific hex character, or that the character is ignored in sequence matching.

Leading characters that are ignored characters are not part of the end condition. Trailing

characters that are ignored characters are part of the end condition.

S7-1200 Programmable controller

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