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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

Data exchanges are handled in the telegram header using Service

Access Points (SAP’s). The SAP tells what data is to be transmitted or

which function is to be performed. Only telegrams that include data fields

use DSAP & SSAP bytes (i.e. SD2 & SD3 telegrams). Recall that SRD

transmission combines an output message with an input response in a

single telegram cycle. The telegram header contains an SSAP (Source

Service Access Point) and/or DSAP (Destination Service Access Point) that

indicates the service(s) to be executed. One exception is the cyclical

Data_Exchange telegram which is performed with the default SAP (SSAP or

DSAP is not provided in its header). Additionally, some telegrams may only

provide a DSAP or SSAP, but not both.

The inclusion of a DSAP or SSAP entry in a request or response

telegram is identified by setting the highest bit in the address byte of the DA

(Destination Address) or SA (Source Address), respectively. Based on the

detected SAP’s, each station is able to recognize which data has been

requested and which response data is to be supplied. ProfiBus DP uses

SAP’s 54 to 62 listed below, plus the default SAP.

SAP SERVICE

Default SAP=0 Cyclical Data Exchange (Write_Read_Data)

SAP54

Master-to-Master SAP (M-M Communication)

SAP55 Change Station Address (Set_Slave_Add)

SAP56 Read Inputs (Rd_Inp)

SAP57 Read Outputs (Rd_Outp)

SAP58 Control Commands to a DP Slave (Global_Control)

SAP59 Read Configuration Data (Get_Cfg)

SAP60 Read Diagnostic Data (Slave_Diagnosis)

SAP61 Send Parameterization Data (Set_Prm)

SAP62 Check Configuration Data (Chk_Cfg)

SAP55 is optional and may be disabled if the slave does not provide

non-volatile storage memory for the station address. Note that SAP’s 56, 57,

and 58 are not enabled until the DP slave assumes the Data_Exchange

state. SAP’s 59, 60, 61, and 62 are always enabled.

Note that the DSAP & SSAP entries in a request telegram are also

included in the response telegram, where DA + SA + DSAP + SSAP in the

response message corresponds to SA + DA + SSAP + DSAP in the request

telegram (content position flips).

This field contains the data for the station at DA (request data), or the

data for the station at SA (response data). DU is generally limited to 32

bytes, but the standard allows for lengths up to 244 bytes (assuming 11

bytes of header information for 255 bytes total).

This field contains the Frame Check Sequence or telegram checksum

(00H..FFH). It is simply the sum of the ASCII bytes of information from DA

to DU modulus 256. Checksum = (DA + SA + FC + DU) mod 256. This is

simply the bytes added together and divided by FFH (255). This is an

integrated function that is normally performed by the ProfiBus ASIC.

Service Access Points

(SSAP & DSAP)

Data Unit (DU)

Frame Check Sequence

(FCS)

1 2 ... 14 15 16 17 18 19 20 21 22 23 24 ... 37 38

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