The protocol Simatic Fetch/Write enables the connection of S7 automation devices with any communication partner.
It provides direct access to the S7 user memory without changes in the user application itself, if applicable.
Only a communication unit (CP) for Ethernet connection or alternatively an onboard Ethernet interface that supports ISOonTCP (RFC1006) as well as the protocol Simatic Fetch/Write
must be available.
An onboard Ethernet interface requires the development of special function modules for the communication in addition to the S7 user program.
This is not necessary with an external communication unit (CP).
The SIMATIC® S7 series supports the services FETCH and WRITE via the protocol ISO-on-TCP only in passive mode, i.e. it operates as a server and does not establish
communications links spontaneously.