10-92
Handling, Diagnostic and Service Functions
MPH-02, MPB-02, MPD-02
DOK-INDRV*-MP*-02VRS**-FK01-EN-P
Structure of the Telegram Header
The SIS telegram header consists of a static and a dynamic part.
Static part of the telegram header
The static part of the telegram header contains 8 byte and is contained in
each SIS telegram.
Byte
Name
Description of the bytes in the static part of the telegram header
1
StZ
Start character: STX (0x02)
2
CS
Checksum byte
The checksum is generated in three steps:
1)
the "CS" byte is cleared
2)
all characters in the telegram are added byte by byte
3)
the negated sum is stored in the "CS" byte
The result of the byte-by-byte addition of all characters in an SIS telegram is always zero!
3
DatL
Data length
The "DatL" byte contains the length of the telegram without the static telegram header.
The total length of an SIS telegram is limited to 255 byte.
Therefore, a maximum of 247 byte of
useful data can be transmitted.
4
DatLW
Data length repetition
5
Ctrl
Control byte
In the control byte, the telegram type and the structure of the dynamic telegram header are
declared:
bit 0…2: number of subaddresses in the dynamic part of the telegram header
bit 3:
specifying whether dynamic telegram header contains "PaketN" (package number) byte
0 => without package number; 1 => with package number
bit 4:
determining the telegram type
0 => command telegram; 1 => reaction telegram
bit 5:
reserved
bit 6:
reserved in command telegrams
in reaction telegrams bit 6 signals a system warning in the slave
bit 7:
reserved in command telegrams
in reaction telegrams bit 7 signals a system error in the slave
6
Dienst
SIS service
The byte specifies the SIS service of the telegrams. Subservices are defined in some SIS
services. In these cases the subservice is specified in the useful data header.
The useful data of the command and reaction telegrams can be defined in a different way for each
SIS service and its subservice.
7
AdrS
Address of the transmitter
in command telegrams:
address of the master, valid from 0 to 126
in reaction telegrams:
address of the slave
8
AdrE
Address of the receiver
in command telegrams:
address of the slave, valid from 0 to 126
address 128: special address for a "point-to-point" connection
Each slave reacts to the special address independent
of its station number.
address 254: collective message to all slaves in the direct
hierarchical level
address 255: collective message to all slaves in the SIS network
below the master
Slave do not respond to collective messages.
in reaction telegrams:
address of the master
Fig. 10-53: SIS telegram header, static part
Courtesy
of
CMA/Flodyne/Hydradyne
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