Siemens Simatic S7 Series System Manual

Communication
8.6 RS485
S7-200 SMART
System Manual, 09/2015, A5E03822230-AC
395
8.6
RS485
An RS485 network is a differential (multi-point) network and can have up to 126 addressable
nodes per network and up to 32 devices per segment. Repeaters are used to segment the
network. Repeaters are not addressable nodes; therefore, they are not included in the count
of addressable nodes, but are counted in the devices per segment.
RS485 allows for data transfer at a high speed (from 100 m at 12 Mbit/s to 1 km at 187.5
Kbit/s).
RS485 can operate with the PPI protocol and Freeport:
● PPI protocol: Can operate on RS485 or RS232 (half-duplex). Possible connections
include:
– PPI protocol devices
– RS485 HMI displays
● Freeport: Can operate on RS485 or RS232 (half-duplex). Possible connections include:
– RS485-compatible devices (for example, a bar code scanner)
– Devices that have RS485 interfaces (for example, a control system)
– Third-party devices using Freeport
– Modems
8.6.1
PPI protocol
Definition
PPI is a master-slave protocol: the master devices send requests to the slave devices, and
the slave devices respond. See the following figure. Slave devices do not initiate messages,
but wait until a master sends them a request or polls them for a response.
Masters communicate to slaves by means of a shared connection which is managed by the
PPI protocol. PPI does not limit the number of masters that can communicate with any one
slave; however, you cannot install more than 32 masters on the network.

Siemens Simatic S7 Series Specifications

General

CPU	Varies by model (e.g., S7-300, S7-400, S7-1200, S7-1500)
Communication Interfaces	PROFIBUS, PROFINET, Ethernet, MPI
Programming	TIA Portal, STEP 7
Programming Languages	LAD, FBD, STL, SCL, GRAPH
I/O Modules	Digital, Analog, Specialty modules available
Operating Temperature	0°C to 60°C (standard models)
Mounting	DIN rail mounting
Operating Voltage	24V DC or 120/230V AC (varies by model)
Protection Class	IP20 (standard models)
Memory	Varies depending on the S7 model. Includes work memory (RAM) for program execution, load memory (EEPROM or Flash) for program storage, and system memory for operating system functions. Memory sizes range from kilobytes to megabytes.