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Communications
6.2 PtP, USS, and Modbus communication protocols
6.2
PtP, USS, and Modbus communication protocols
The CPU supports the PtP protocol for character-based serial communication, in which the
user application completely defines and implements the protocol of choice.
PtP communication is serial communication that support a variety of baud rates and parity
options. STEP 7 Basic provides libraries of instructions that you can use in programming
your application. These libraries provide PtP communication functions for the following
protocols:
● USS drive protocol (RS485 only)
● Modbus RTU Master protocol
● Modbus RTU Slave protocol
Communication modules for PtP
A communication module (CM) provides the interface for PtP communications. There is a
CM for RS232 and a CM for RS485. You can connect up to three CMs (of any type) to the
CPU. Each CM has the following characteristics:
● Isolated port
● Supports the PtP, USS (RS485 only) and Modbus protocols
● Configured and programmed through extended instructions and library functions
● Displays transmit and receive activity by means of LEDs
● Displays a diagnostic LED
● Powered by the CPU, with no external power connection required
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PtP enables a wide variety of possibilities:
• The ability to send information directly to an
external device such as a printer
• The ability to receive information from other
devices such as barcode readers, RFID
readers, third-party camera or vision
systems, and many other types of devices
• The ability to exchange information, sending
and receiving data, with other devices such
as GPS devices, third-party camera or
vision systems, or radio modems
Manual, 05/2009, A5E02486774-01
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