Siemens SPC3 Specifikace stáhnout pdf (Strana 33)

Introduction To ProfiBus DP

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Acromag, Inc. Tel:248-624-1541 Fax:248-624-9234 Email:sales@acromag.com http://www.acromag.com

After parameterization and configuration have been accomplished, the

master can start exchanging cyclical I/O data with the slaves. The following

services are available in data exchange mode: Read_Inp (read the inputs of

any slave), Read_Outp (read the outputs of any slave), and Data_Exchange

(send and receive data to the slave parameterized and configured by the

master). A slave will automatically check the transferred output data,

respond with the input data, and generate a message if it detects a

discrepancy.

The Data_Exchange function refers to the cyclic transfer of I/O data and

possible diagnostic information between slaves and their class 1 masters.

Recall that ProfiBus may use SRD transmission (Send and Request Data

with Acknowledge) that allows it to send output data and receive input data

in a single message/response cycle. With Data_Exchange, the number of

inputs and outputs has already been defined in the configuration data at the

system startup. In Data_Exchange mode, the master cyclically sends the

output data to the slave and receives input data (if present) in return. If the

slave is purely an output device (no input data to return), it responds with

“E5H” in its response data field (a short acknowledge). Unlike every other

telegram which has 11 bytes of header information, the Data_Exchange

telegram has only 9 bytes of header information as it uses the default SAP

(implied), with the DSAP & SSAP bytes are dropped from the telegram

header. In Data_Exchange mode, the slave will allow the reconfiguration of

I/O data to occur (Chk_Cfg), but will not permit reparameterization.

Data_Exchange Send Output or Receive Input Data Telegram

SD LE LEr SD DA SA FC DU FCS ED

68H X X 68H 8x 8x X X.. X 16H

Recall that with data exchange, the telegram header has only nine

bytes since the default SAP is used and the DSAP & SSAP bytes are

dropped from the telegram header. This is indicated by the most significant

bit of the DA & SA bytes which are clear (0). If the MSB is set to 1 in the DA

& SA bytes, this indicates a DSAP & SSAP follows in the telegram header.

The DU contains from 1 to 244 bytes of user data to be transferred (output

data and/or input data).

In Data_Exchange mode, any master can read the I/O data of any slave

at any time using the “Read_Inputs” and “Read_Outputs” telegrams. These

telegrams have the same structure as the cyclic Data_Exchange telegram,

but include the DSAP and SSAP bytes. For these telegrams, the MSB of the

DA & SA bytes will be set to “1” to indicate that a DSAP & SSAP byte follows

in the telegram header.

Read_Inp Telegram – SAP 56

The master can use this telegram to

asynchronously

read the input

data (Inp_Data) of any slave in Data_Exchange mode.

SD LE LEr SD DA SA FC DSAP SSAP FCS ED

68H 05H 05H 68H 8x 8x X 38H

(56)

3EH

(62)

X 16H

Data Exchange State

1 2 ... 28 29 30 31 32 33 34 35 36 37 38

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