Basic Characteristics And Parameters Of The Serial Sensor Interface; Description Of Protocol; Telegram Structure - Sensopart FT 50 RLA-70-L8 Instructions De Service Et De Montage

8.1

Basic characteristics and parameters of the serial sensor interface

The serial interface of the sensor has the following characteristics:
Hardware
Data transfer rate
Stop bits
Parity
Bits / Byte
Access method
Sensor address
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 400 to 800 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
Selection bit
General telegram structure
A complete telegram, from both the master and the slave, consists of at least 4 bytes and has the following structure:
1. Byte
2. Byte
3. Byte
4. Byte ... (n-1). Byte
n. Byte (last Byte)
The 1st byte always included the sensor address. In addition, it is characterized by the selction 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 address 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:
62
Fixed factory configuration
RS485, half-duplex
Pin1 Data+ (Y/A), Pin5 Data- (Z/B)
38400 Baud
1
no
8
Master / Slave
(the sensor behaves as a slave)
D6 D5
7 data bits / address bits
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
D4 D3
FT 50 RLA Disctance sensor - GB - 068-13671 - 20.04.2009-05
Mounting and
operating instructions
modifiable
1
D2 D1
Reply sensor
Reply (see reply telegram, below)
D7=0
D0