The digital signal is represented by a "0" or "1" ( + / - ). Each pulse is of the same length, irrespective of it being a NULL or ONE. The complete message is subdivided into 11 bit data strings.

Each string consists of the same number of pulses of equal strings : one start bit, 8 data bits, one parity bit and one stop bit. The data bits and parity bit may either take the low level state ( logical 0 ) or high level state ( logical 1 ).

The length of the information within the message is variable. In addition to this information block of variable length, the message has also a header and address block of fixed length.

The telegram with variable length is used for data transmission of user data between master station and slave station and in the opposite direction.

The station number, 7 bit binary coded number gives the possibility to address up to 127 substations ( station 1... 127 ). The master station has the station number = 0.

The TGE bit is a 1 bit marker used in monitoring direction and shows that a substation in polling mode has transmitted its last message. ( only used in multi-point systems )

The MSC enables the possibility that any spontaneous message which one has been corrupted during transmission can be repeated. The substation retains the last 30 records in case it receives a repeat request ( CDH 02 ).

During start-up the substation transmits all messages with MSC = 31, until the masterstation has sent a start-up acknowledgement command ( CDH 03 ). In the subsequent normal operation the messages of the substation contain a MSC from 1 up to 30.

Spontaneous and housekeeping messages always increase the MSC number, interrogated messages may or may not increase the MSC number ( parametrizable in the substation ).

For the Messages in control direction the MSC = 0 is only used.

The overflow bit is set by the substation if the MSC-Buffer is not acknowledged ( CDH 02 ) and therefore overflows.

The Data Type indicates in monitoring direction the source of the data and in control direction the destination of the data.

DA = 0 : Housekeeping   ( CDH.. / MDH.. )
DA = 1 : Spontaneous process messages  ( CD.. / MD.. )
DA = 2 : Cyclic process messages   ( only in monitoring direction )
DA = 3 : Polled process messages  ( indications during general interrogation )

The 10 bits allow an adressing of 1024 bytes in monitoring and control direction. Each information byte in a system, main- or subsystem, is indicated by a record number within the 1024 byte input- or output area.

If a message is transmitted with an information block that consists of just one information byte, then the information byte location number is identical to the message number. If however, the information block consits of more than 1 byte then the number of the first byte is the message number and increases for the following bytes continously by one.

The record length shows the number of bytes in the information block. The actual length is represented in 2 bits ( RL ), the 3rd bit is a compression bit ( C ). If a message has the C bit set, this means that the useful information block is either 9, 36 or 72 bits long.

Indicates in monitoring direction the source and in control direction the destination of information. ( system of the substation )

System = 0       : Main System ( MASY )
System = 1... 6 : Subsystem 1... 6 ( SUSY 1... 6 )
System = 7       : reserved for internal use

Unfortunately the TypID is not recognizable out of the SINAUT 8-FW message. In the process-system it is associated with the message number. In order to display in LIAN 98 the particular informations ( messages, measurands, ... ) not only e.g. hexadecimal but also in a easily readable plain text, an unambiguous TypID is defined. Organizational messages and messages in control direction are not affected.

Via the <parameter list> the correct TypeID can be assigned to the telegram number. The TypeID value ZERO is not used.

The following table shows the type identification numbers for process information in control- and monitoring direction defined in LIAN 98.