Description Of Protocol; Telegram Structure - Sensopart FT 50 C S1 Série Instructions De Service Et De Montage

8.2

Description of protocol

• The data transfer protocol is bus-compatible.
• The sensor only sends data on request. The sensor has an address within the range 1 to 127
(factory setting = 1).
• A data transfer cycle consists of a command telegram addressed to the sensor by the master and the sensor's
reply telegram.
• The sensor begins with the reply telegram within 500 µs after receipt of the command telegram.
8.3

Telegram structure

Each byte consists of a selection bit (D7) and 7 data or address bits (D0 to D6).
Byte structure
D7 D6
Selection bit 7 data bits / address bits
General telegram structure
A complete telegram, from both the master and the slave, consists of at least 4 bytes and has the following structure:
1st byte
2nd byte
3rd byte
4th byte to (n-1) byte
n byte (last byte)
The 1st byte always included the sensor address. In addition, it is characterized by the selection bit (D7 = 1). This
means that this byte is decimal: always „address +128". The selection bit is not set (D7=0) with any other bytes.
When the master sends a byte with a set selection bit, a new data transfer cycle is started, regardless of
whether the previous cycle has been completed.
The last byte is the check sum which is formed from the bitwise exclusive disjunction of all previous bytes. When
calculating the check sum, the 8
bit)  129 = 1! If the sensor adress is changed, the check sum for each command must be recalculated.
In the command telegram, the 3rd byte can adopt the values listed in the chapter 8.5 „Examples for master
commands".
In the sensor's reply telegram, the 3rd byte (reply) can only adopt the following values:
Possible reply telegram from sensor
Decimal Hex.:
89 59
78 4E
12 bit and 7 bit data is transferred in the parameter bytes (4th byte to (n-1) byte). The following formats are used:
48
D5 D4
Master
Address 1 (to 127) corresponds with 129 (to 255), as the selection bit of the
1st byte (D7) =1
Length of telegram, number of all bytes (4 to 127), D7=0
Command (see „Overview of master
commands") D7=0
Parameter (see parameter bytes, below) D7=0
Check sum exclusive OR of byte 1 to byte n-1, D7=0
bit (selection bit D7) must be deducted from the first byte (address and selection
th
Meaning
Command has been carried out
Command could not be carried out;
Possible causes: check sum or parameter / command incorrect
operating instructions
D3 D2 D1
Reply sensor
Reply (see reply telegram, below)
D7=0
FT 50 C...S1 Colour sensor - GB - 068-13821 - 10.10.2011-04
Mounting and
D0