Manual VIPA CPU 21x Chapter 9 Deployment CPU 21xSER-1
HB103E - Rev. 05/45 9-5
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 connection
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:
• Multi point connection
• Master-Slave access procedure
• Single-Master-System
• Max. 32 participants
• Simple and secure telegram frame
You may connect 1 master and max. 31 slaves at the bus where the single
slaves are addressed by the master via an address sign in the telegram.
The communication happens exclusively in half-duplex operation.
After a send command, the acknowledgement telegram must be read by a
call of the SFC 218 SER_RCV.
The telegrams for send and receive have the following structure:
Master-Slave telegram
STE LGE ADR PKE IND PWE STW HSW BCC
02h H L H L H L H L H L
Slave-Master telegram
STE LGE ADR PKE IND PWE ZSW HIW BCC
02h H L H L H L H L H L
where STX: Start sign STW: Control word
LGE: Telegram length ZSW: State word
ADR: Address HSW: Main set value
PKE: Parameter ID HIW: Main effective value
IND: Index BCC: Block Check Character
PWE: Parameter value
A request can be directed to a certain slave ore be send to all slaves as
broadcast message. For the identification of a broadcast message you
have to set Bit 5 to 1 in the ADR-Byte. Here the slave addr. (Bit 0 ... 4) is
ignored. In opposite to a "normal" send command, the broadcast does not
require a telegram evaluation via SFC 218 SER_RCV. Only write
commands may be send as broadcast.
USS
Broadcast with set
Bit 5 in ADR-Byte
01234
567
Broadcast
1
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