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DPC31 HW

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DPC31 HW Description

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5 Communication Functions of the Sequential Control System

PROFIBUS Layer2 and the DP slave module are implemented in the sequential control system. Layer2 is

composed of a MAC (media access control) part and an FLC (interface services) part. In the following, the

Layer2 module is simply called MAC module. The user can influence only the cells that are described here.

5.1 Setting Up the DP Buffer Structures

To set up the DP buffers, the corresponding buffer pointers are entered in the organizational parameters and

the buffers lengths are entered in the buffers. All pointers are 8-Bit segment buffer pointers. During access,

the sequential control system adds an 8-Bit offset address to the segment address that has been shifted by

5-Bits (x32) (result: 13-Bit physical address). Therefore, the list and buffer start addresses, have a

granularity of 32 bytes.

5.1.1 Structure of the Buffers

Figure 5.1-1 shows the structure of the request buffers and response buffers for the DPS SAPs

SAP Buffers

Header Field: Reserved

Length_Data_Buffer

Reserved

Data Field: Data 0

Data 1

.....

Data 243

Figure 5.1-1:

Structure of the SAP Buffers

Length_Data_Buffer:

This value specifies the length of the data field in the request buffer. If the net data length of the

request message is larger than the available buffer length, the MAC responds with “No Resource’.

Except for the DIN and Dout buffers, the user must enter the length in all buffers!

5.1.2 Request Interface for DPS (Instruction Queue)

User requests to the DPS module are transferred via a request interface. This request list is a polling list

onto which the user transfers communication requests. Figure 5.1-2 shows the organization of the

Instruction_Queue. With each entry (5 bytes respectively), the user must also transfer the command to the

sequential control system. This is done with a write operation with any data value to the register cell

‘User_InstQ_Write Cmd’. The organization of the Instruction_Queue includes the following parameters:

InstQ_Base Ptr: The Instruction_Queue segment pointer

InstQ_Length: Describes the length of the Instruction_Queue and is a multiple of the length of an

entry (n*5)

InstQRd Ptr: An Offset_Pointer which points to the next entry that is to be read (and is managed

by the DPC31)

InstQ_Wr Ptr: An Offset_Pointer which points to the next free entry (and is managed by the user)

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Siemens SPC3 Specifiche Pagina 23