Point-To-Point Instructions; Common Parameters For Point-To-Point Instructions - Siemens SIMATIC S7 System Manual
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Point-to-Point (PtP) communications
8.7 Point-to-Point instructions
If you set the cycle time for the OB to provide for two executions within the timeout period of
the master, the user program should receive transmissions without missing any.
8.7
Point-to-Point instructions
8.7.1
Common parameters for Point-to-Point instructions
Communication module LED behaviors
There are three LED indicators on the Communication module (CM):
● Diagnostic LED: This LED flashes red until it is addressed by the CPU. After the CPU
● Transmit LED: This LED is located above the receive LED. The transmit LED illuminates
● Receive LED: This LED illuminates when data is being received by the communication
Bit time resolution
Several parameters are specified in a number of bit times at the configured baud rate.
Specifying the parameter in bit times allows the parameter to be independent of baud rate.
All parameters that are in units of bit times can be specified to a maximum number of 65535.
However, the maximum of amount of time that can be measured by a S7-1200 is 8 seconds.
REQ input parameter
Many of the Point-to-Point (PtP) instructions use a REQ input that initiates the operation on a
low to high transition. The REQ input must be high (TRUE) for one execution of an
instruction, but the REQ input can remain TRUE for as long as desired. The instruction will
not initiate another operation until it is called with the REQ input FALSE so that the
instruction can reset the history state of the REQ input. This is required so that the
instruction can detect the low to high transition to initiate the next operation.
When you place a PtP instruction, you are prompted to identify the instance DB. Use a
unique DB for each type of PtP instruction. That is, all SEND_PTP instructions for a given
port should have the same instance DB, but SEND_PTP and RCV_PTP must have different
instance DBs. This ensures that inputs such as the REQ are properly handled by each
instruction.
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powers up, it will check for modules and address the CM module. The Diagnostic LED will
begin to flash green. This means that the CPU has addressed the CM, but has not yet
provided configuration to the CM. The configuration is downloaded to the module when
the program is downloaded to the CPU. After a download to the CPU, the Diagnostic LED
on the communication module should be a steady green.
when data is being transmitted out the communication port.
port.
S7-1200 Programmable controller
System Manual, 11/2009, A5E02486680-02
- Quick Links:
- Introducing the S7-1200 Plc
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