Siemens SPC3 Specifications download pdf (Page 14)

Introduction To ProfiBus DP

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Most configuration tools also allow you to permanently store user

parameters and configuration bytes which the master will automatically send

to the slave during system startup.

ProfiBus DP uses two types of transmission services in sending

message telegrams that are defined in Layer 2 (The Data Link Layer) of the

ISO/OSI model and summarized below:

SRD (Send and R

equest Data with acknowledge)

With SRD, data is sent and received in one telegram cycle. That is, the

master sends output data to the slave and receives input data from the slave

in its response (if applicable) within a specified period of time. The important

thing to remember about this service, is that a master may send output data

to a slave and request input data from the slave in its response, all in a

single telegram cycle. This is the transmission service most often used in

ProfiBus DP that makes the data exchange very efficient for mixed I/O

devices.

SDN (Send D

ata with No acknowledge)

This service is used when a message must be sent simultaneously to a

group of slaves (multi-cast), or all slaves (broadcast). Slaves do not respond

or acknowledge broadcast or multi-cast messages.

A third type of transmission service used in ProfiBus FMS is SDA (Send

Data with Acknowledge), with data sent to a master or slave and a short

acknowledgement sent in response. This is not used in ProfiBus DP and is

not covered here.

All ProfiBus characters are comprised of 11 bits (1 start bit + 8 data bits

+ 1 even parity bit + 1 stop bit). ProfiBus DP exchanges data in NRZ code

(Non Return to Zero). That is, the signal form of binary “0” or “1” does not

change during the duration of the bit. If nothing is being transmitted, the idle

state potential on the line is “1”. A start bit causes the line to go to “0”.

ProfiBus NRZ-Coded Character Frame (Even Parity)

Start D0D1D2D3D4D5D6 D7ParityStop

“0”

0123456 7

even “1”

← LSB ←←←←←←MSB ←←

This character frame applies to all data/character bytes, including the

telegram header bytes. When messages are transmitted on ProfiBus serial

networks, each character or data byte is sent in the order of least significant

bit (lsb) to most significant bit (msb), as shown above. For word transfer

(more than 1 byte), the high byte is transmitted first, followed by the low byte

(Big-Endian/Motorola format).

TYPES OF

TRANSMISSION

PROFIBUS DP

DATA CHARACTER

FORMAT

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 ... 37 38

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Siemens SPC3 Specifications Page 14

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