User Manual

Communication via RS485
5.3 Communication via USS
Fieldbuses
114 Function Manual, 04/2018, FW V4.7 SP10, A5E34229197B AE
5.3.2
Telegram structure
Overview
A USS telegram comprises a series of elements with a defined sequence. Each element
contains 11 bits.
Figure 5-2 Structure of a USS telegram
Telegram part
Description
Start delay / re-
sponse delay
There is always a start and/or response delay between two telegrams.
Time-out and other errors (Page 123)
STX
An ASCII character (02 hex) indicates the beginning of the message.
LGE The telegram length "LGE" is calculated as follows:
LGE = user data (n bytes) + ADR (1 byte) + BCC (1 byte)
ADR
• Bit 7 = 0: Normal data exchange.
Bit 7 =1, to transfer telegrams that require a net data structure different
from the device profile.
• Bit 6 = 0: Normal data exchange.
Bit 6 = 1: Testing the bus connection: The converter returns the telegram
unchanged to the master.
• Bit 5 = 0: Normal data exchange.
(Bit 5 = 1: Not supported in the converter.)
• Bits 0 ... 4: Address of the converter.
Net data
User data range of the USS telegram (Page 115).
BCC Checksum (exclusive or) across all telegram bytes – with the exception of
BCC.