Siemens SPC3 Specifications download pdf (Page 18)

Introduction To ProfiBus DP

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This byte specifies the length of a telegram with variable data length

(i.e. SD2 Telegrams) from the DA byte to the end DU byte (range is DU+5b

to 249). Note that the length of the DU is generally limited to 32 bytes, but

the standard allows for lengths up to 244 bytes. LE is repeated in the LEr

field for redundant data protection.

The master device addresses a specific slave device by placing the 8-

bit slave address in the DA address field of the telegram (Destination

Address). It includes its own address in the SA address field (Source

Address). Valid addresses are from 0-127 (00H..7FH). Address 126 is

reserved for commissioning purposes and may not be used to exchange

user data. Address 127 is reserved as the broadcast address, which all

slave devices on a network recognize. When the slave responds, it will

place its own address in the source address field of its response to let the

master know which slave is responding, and it will place its assigned

master’s address in the destination address field of its respone. Recall that

a slave does not issue a response to broadcast messages (address 127).

Note that 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. This

may look like an address greater than 127, but only the lower 7 bits of the

DA and SA contain the actual address.

The Function Code (FC) or Frame Control field specifies the type of

telegram (request, response, acknowledgement), type of station (passive or

active/slave or master), priority, and telegram acknowledgement (successful

or unsuccessful) as follows:

ProfiBus DP Function Codes for Request Telegrams

FC Code Function (The MSB in FC = 1)

4 SDN low (Send Data with No acknowledge)

6 SDN high (Send Data with No acknowledge)

7 Reserved/Request Diagnostic Data

9 Request FDL Status With Reply

12 SRD low (Send and Request Data with acknowledge)

13 SRD high (Send and Request Data with acknowledge)

14 Request ID With Reply

15 Request LSAP Status With Reply

ProfiBus DP Function Codes for Acknowledgement Telegrams

FC Code Function (The MSB in FC = 0)

0 ACK Positive

1 ACK Negative (FDL/FMA1/2 user error UE, interface error)

2 ACK Negative (No resource/memory space for Send Data (RR).

3 ACK Negative (No service activated (RS), SAP not activated).

8 Response FDL/FMA ½ Data low and Send Data OK)

9 ACK Negative (No response FDL/FMA1/2 Data & Send Data OK).

10 Response FDL Data High and Send Data OK.

12 Response FDL Data Low, No resource for Send Data.

13 Response FDL Data High Resource For Send Data.

Length of Telegram

(LE & LEr)

Destination Address &

Source Address

(DA & SA, 00H..7FH)

Function Code or

Frame Control (FC)

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 37 38

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Siemens SPC3 Specifications Page 18

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