SPC3 PROFIBUS Interface Center
SPC3 Hardware Description V1.1 Page 11
Copyright (C) Siemens AG 1998. All rights reserved. 12/99
4 Memory Allocation
4.1 Memory Area Distribution in the SPC3
The figure displays the division of the SPC3 1.5k internal address area.
The internal latches/register are located in the first 21 addresses. The internal latches/register either come
from the controller or influence the controller. Certain cells can be only read or written. The internal work
cells to which the user has no access are located in RAM at the same addresses.
The organizational parameters are located in RAM beginning with address 16H. The entire buffer structure
(for the DP-SAPS) is written based on these parameters. In addition, general parameter setting data (station
address, Ident no., etc.) are transferred in these cells and the status displays are stored in these cells (global
control command, etc.).
Corresponding to the parameter setting of the organizational parameters, the user-generated buffers are
located beginning with address 40H. All buffers or lists must begin at segment addresses (48 bytes
segmentation).
Address Function
000H Processor parameters internal work cells
Latches/register
(22 bytes)
016H Organizational
parameters
(42 bytes)
040H DP- buffer: Data In (3) *
Data Out (3) *
Diagnostics (2)
Parameter setting data (1)
5FFH Configuration data (2)
Auxiliary buffer (2)
SSA-buffer(1)
Figure 4.1: SPC3 Memory Area Distribution
Caution:
The HW prohibits overranging the address area. That is, if a user writes or reads past the memory
end, 400H is subtracted from this address and the user therefore accesses a new address. This
prohibits overwriting a process parameter. In this case, the SPC3 generates the RAM access
violation interrupt. If the MS overranges the memory end due to a faulty buffer initialization, the same
procedure is executed.
* Data In is the input data from PROFIBUS slave to master
Data out is the output data from PROFIBUS master to slave
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