Sensopart FT 50 RLA 220-L8, Монтаж и эксплуатация, Страница: 62 / 122

FT 50 RLA Disctance sensor - GB - 068-13671 - 20.04.2009-05
Mounting and
operating instructions
62
8.1 Basic characteristics and parameters of the serial sensor interface
The serial interface of the sensor has the following characteristics:
Fixed factory configuration modifiable
Hardware RS485, half-duplex
Pin1 Data+ (Y/A), Pin5 Data- (Z/B)
Data transfer rate 38400 Baud
Stop bits 1
Parity no
Bits / Byte 8
Access method Master / Slave
(the sensor behaves as a slave)
Sensor address 1
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 D6 D5 D4 D3 D2 D1 D0
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:
Master Reply sensor
1. Byte Address 1 (to 127) corresponds with 129 (to 255), as the selection bit of the
1st byte (D7) =1
2. Byte Length of telegram, number of all bytes (4 to 127), D7=0
3. Byte Command (see “Overview of master
commands”) D7=0
Reply (see reply telegram, below)
D7=0
4. Byte ... (n-1). Byte Parameter (see parameter bytes, below) D7=0
n. Byte (last Byte) Check sum exclusive OR of byte 1 to byte n-1, D7 = 0.
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 „a128”. 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 th bit (selection bit D7) must be deducted from the first byte (address and selection
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: