315-4PN33

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 termi-

nate the connection (DLE duplication). The DLE duplica-

tion is reversed in the receiving station.

The 3964R procedure requires that a lower priority is

assigned to the communication partner. When communi-

cation 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

n Max. 32 participants

n Simple and secure telegram frame

It is essential:

n You may connect 1 master and max. 31 slaves at the bus

n The single slaves are addressed by the master via an address

n The communication happens exclusively in half-duplex operation.

n After a send command, the acknowledgement telegram must be

read by a call of the FC/SFC 218 SER_RCV.

The telegrams for send and receive have the following structure:

Master slave telegram

STX LGE ADR PKE IND PWE STW HSW BCC

02h H L H L H L H L H L

Slave master telegram

STX LGE ADR PKE IND PWE ZSW HIW BCC

02h H L H L H L H L H L

USS

VIPA System 300S Deployment PtP communication

Protocols and procedures

HB140 | CPU | 315-4PN33 | GB | 14-43 97