Watson-Marlow MM420 - Manual (Page 103)

Issue 10/06 3 Functions
MICROMASTER 420 Operating Instructions
6SE6400-5AA00-0BP0 103
The telegram has the following structure:
Each telegram begins with the start character STX (= 02 hex), followed by the
length information (LGE) and the address byte (ADR). The net characters then
follow. The telegram is terminated by the BCC (Block Check Character).
For single-word data (16 bit) in the net data block (= net character block), the
high byte (first character) is always sent and then the low byte (second
character).
The same applies to double-word data: the high word is sent first followed by
the low word.
The necessary settings / parameter assignments must be made both at the
master as well as at the slave and can no longer be changed in bus operation.
The protocol does not identify tasks in the net characters. The contents of the
net characters/data for the MICROMASTER drives is discussed in Section
3.7.1.2 "Structure of the net data".
n net characters
STX LGE ADR 1. 2. n BCC
Fig. 3-32 Telegram structure
Information is coded as follows:
Abbreviation Significance Size Explanation
STX Start of text ASCII characters 02 hex
LGE Telegram length 1 byte Contains the telegram length
ADR Address 1 byte Contains the slave address and the
telegram type (binary coded)
--- Net characters Each one byte Net data, contents are dependent on
the request
BCC Block check
character
1 byte Data security characters