Program instructions
7.3 Communication
S7-200 SMART
202 System Manual, V2.3, 07/2017, A5E03822230-AF
The Transmit instruction lets you send a buffer of one or more characters, up to a maximum
of 255. The following figure shows the format of the Transmit buffer.
Number of bytes to transmit
Characters of the message
If an interrupt routine is attached to the transmit complete event, the CPU generates an
interrupt (interrupt event 9 for port 0 and interrupt event 26 for port 1) after the last character
of the buffer is sent.
You can transmit without using interrupts (for example, sending a message to a printer) by
monitoring SM4.5 (port 0) or SM4.6 (port 1) to signal when transmission is complete.
You can use the Transmit instruction to generate a BREAK condition by setting the number
of characters to zero and then executing the Transmit instruction. This generates a BREAK
condition on the line for 16-bit times at the current baud rate. Transmitting a BREAK is
handled in the same manner as transmitting any other message, in that a Transmit interrupt
is generated when the BREAK is complete and SM4.5 or SM4.6 signals the current status of
the Transmit operation.
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