The 3964R procedure controls the data transfer of a point-to-point link
between the CPU and a communication partner
. The procedure adds
control characters to the message data during data transfer. These
control characters may be used by the communication partner to
verify the complete and error free receipt.
The procedure employs the following control characters:
n STX: Start of Text
n DLE: Data Link Escape
n ETX: End of Text
n BCC: Block Check Character
n NAK: Negative Acknowledge
You may transfer a maximum of 255byte per message.
Procedure
When a DLE is transferred as part of the information it
is repeated to distinguish between data characters and
DLE control characters that are used to establish and
to terminate the connection (DLE duplication). The
DLE duplication is reversed in the receiving station.
The 3964R procedure requires that a lower priority is
assigned to the communication partner
. When commu-
nication partners issue simultaneous send commands,
the station with the lower priority will delay its send
command.
The USS protocol (Universelle serielle Schnittstelle = universal serial
interface) is a serial transfer protocol defined by Siemens for the drive
and system components. This allows to build-up a serial bus connec-
tion between a superordinated master and several slave systems.
The USS protocol enables a time cyclic telegram traffic by presetting
a fix telegram length.
The following features characterize the USS protocol:
n Multi point connection
n Master slave access procedure
n Single master system
3964
USS
VIPA System 300S Deployment PtP communication
Protocols and procedures
HB140 | CPU | 314-6CF03 | GB | 16-43 185
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