As Start-res. End-ID all Hex values from 01h to 1Fh are permissible. Characters above
1Fh are ignored. In the user data, characters below 20h are not allowed and may cause
errors. The number of Start- and End-IDs may be dif
ferent (1 Start, 2 End res. 2 Start, 1
End or other combinations). For not used start and end characters you have to enter FFh
in the hardware configuration.
Message structure:
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 dis-
tinguish 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 communication partners issue simulta-
neous 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 connection between a superordinated master and several slave sys-
tems. The USS protocol enables a time cyclic telegram traf
fic by presetting a fix telegram
length.
3964
USS
VIPA System MICRO
Option: PtP communication
Protocols and procedures
HB400 | CPU | M13-CCF0000 | en | 16-47 162
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