Basic Characteristics And Parameters Of The Serial Sensor Interface; Description Of Protocol; Telegram Structure - Balluff BOD 26K LB04-S115-C Instructions De Service Et De Montage

INFORMATION
If several sensors are connected via the RS485 bus, reflections can occur which may impair
transmission. At the end of the RS485 bus, the cable must therefore be fitted with a resistor
corresponding to the characteristic resistance of the used cable (normally 120 Ohm).
If a sensor is set as master or slave, communication with the PC is not possible.
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 includes 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.
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.
D4 D3
No. 834826 E Edition 1310; Replaces edition 1111; Subject to modification
Mounting and
operating instructions
Modifiable
1
D2 D1
Reply sensor
Reply (see reply telegram, below)
D7=0
D0