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:
S
tart of
T
e
x
t
n
DLE:
D
ata
L
ink
E
scape
n
ETX:
E
nd of
T
e
x
t
n
BCC:
B
lock
C
heck
C
haracter
n
NAK:
N
egative
A
c
k
nowledge
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 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 (
U
niverselle
s
erielle
S
chnittstelle = 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
3964
USS
VIPA System 300S
Deployment PtP communication
Protocols and procedures
HB140 | CPU-SC | 312-5BE13 | GB | 15-50
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