Siemens Simatic S7 Series System Manual

Program instructions
7.3 Communication
S7-200 SMART
System Manual, 09/2015, A5E03822230-AC
183
Start and End conditions for the Receive instruction
The Receive instruction uses the bits of the receive message control byte (SMB87 or
SMB187) to define the message start and end conditions.
Note
If there is traffic present on the communications port from other devices when the Receive
instruction is executed, the receive message function could begin receiving a character in
the middle of that character, resulting in a possible parity or framing er
ror and termination of
the receive message function. If parity is not enabled the received message could contain
incorrect characters. This situation can occur when the start condition is specified to be a
specific start character or any character, as desc
ribed in item 2 and item 6 below.
The Receive instruction supports several message start conditions. Specifying a start
condition involving a break or an idle line detection avoids the problem of starting a message
in the middle of a character by forcing the receive message function to synchronize the start
of the message with the start of a character before placing characters into the message
buffer.

Siemens Simatic S7 Series Specifications

General

CPU	Varies by model (e.g., S7-300, S7-400, S7-1200, S7-1500)
Communication Interfaces	PROFIBUS, PROFINET, Ethernet, MPI
Programming	TIA Portal, STEP 7
Programming Languages	LAD, FBD, STL, SCL, GRAPH
I/O Modules	Digital, Analog, Specialty modules available
Operating Temperature	0°C to 60°C (standard models)
Mounting	DIN rail mounting
Operating Voltage	24V DC or 120/230V AC (varies by model)
Protection Class	IP20 (standard models)
Memory	Varies depending on the S7 model. Includes work memory (RAM) for program execution, load memory (EEPROM or Flash) for program storage, and system memory for operating system functions. Memory sizes range from kilobytes to megabytes.