Transmission Protocol - Pepperl+Fuchs 3RG7256-3NQ00-PF Instructions De Service Et De Montage

Transmission protocol

Transmission frame
The bus­compatible RS 485 interface of 3RG7256­3NQ00­PF operates in half­duplex mode (1 Stopbit, no parity).
As a rule, the distance sensor is a slave and only sends data when addressed by a higher ranking control system
(master) except difference measuring.
A baudrate of 38,4 KBaud and the following protocol must be observed for data transmission:
• 1 selection bit (MSB) + 7 data / address bit
Procedure:
When the address bit has been set, the sensor compares the bus address with its own. If they match, the device
interprets all further data and sends an appropriate feedback signal.
The structure of the transmission frame is as follows:
1 st byte
Request from master
Address of slave
Answer from slave
Address of slave
Slave answers:
Address of slave * 1
2
Address of slave *
3
Address of slave *
Length = Number of characters incl. checksum and address byte
Command = See table of bus commands on page 41
Parameters = Parameter byte 0 to n, depending on command. The slave sends the requested data
in this range.
Checksum = Exclusive OR of all characters sent incl. address byte
1
* is sent when an error in checksum or framelength or an unknown / unvalid parameter or command occurs.
2
* is sent when the command has been carried out.
3
* is sent when parameters have been queried.
40
2 nd byte 3 rd byte
Length Command
Length Command
4 N
4 Y
4 + n Y
3RG7256­3NQ00­PF Distance sensor ­ 068­13787 / 45­3489 ­ Stand: 03/2011
MSB 6 ..... 1 LSB
address bit 7 data / address bits
4 th Byte...(n-1).Byte
Parameter(s)
Parameter(s)
Checksum
Checksum
st nd
1 parameter, 2 parameter,
rd
3 parameter, ..., n parameter
Mounting and
operating instructions
Last byte
Checksum
Checksum
Checksum