Technical data
PROFIBUS networks
1.2 Basics of the PROFIBUS network
PROFIBUS Network Manual
System Manual, Edition 04/2009, C79000-G8976-C124-03
19
S7 protocol
All SIMATIC S7 and C7 controllers have integrated S7 communication services that allow
the user program to read or write data. The S7-400 controllers use SFBs, the S7-300 or C7
controllers use FBs. These functions are available regardless of the bus system used, so
that you can use S7 communication via Industrial Ethernet, PROFIBUS or MPI.
Benefits:
The S7 protocol is supported by all available S7 controllers and communications processors.
PC systems with suitable hardware and software also support communication with the S7
protocol.
● Not dependent on the bus medium (PROFIBUS, Industrial Ethernet (ISO-on-TCP), MPI)
● Can be used with all S7 data areas
● Transfer of up to 64 kbytes in one job
● Layer 7 protocol handles acknowledgment of data records automatically
● Low processor and bus load when transferring larger amounts of data because it is
optimized for SIMATIC communication
1.2.5 Transmission mode
1.2.5.1 Physical transmission techniques
Physical transmission techniques
The physical transmission techniques used depend on the SIMATIC NET PROFIBUS
transmission medium:
● RS485 for electrical networks on shielded, twisted-pair cables
● Optical techniques according to IEC 61158-2 Section 23 on fiber-optic cables
● MBT transmission technique complying with IEC 61158-2 for intrinsically safe and non-
intrinsically safe electrical networks in process control (PROFIBUS PA) based on
shielded, twisted-pair cables.
1.2.5.2 Transmission techniques according to EIA standard RS485
EIA standard RS-485
The RS485 transmission technique corresponds to balanced data transmission as specified
in the
EIA standard RS485 (Page 337). This transmission technique is mandatory in
IEC 61158-2 / EN 61158-2 for data transmission on twisted-pair cables.
The medium is a shielded, twisted pair cable.
The bus cable is terminated at both ends with the characteristic impedance. Such a bus
cable terminated at both ends is known as a segment.