Communications
6.2 PtP, USS, and Modbus communication protocols
Easy Book
76
Manual, 05/2009, A5E02486774-01
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 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
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