Siemens ERTEC200 - Manual (Page 76)

7.1 Page Range Setting
The page size of each page is set in the PAGEx_RANGE_HIGH and PAGEx_RANGE_LOW range registers (x = 0 to 3).
Together, the two page range registers yield a 32-bit address register. The size of the page varies between 256 bytes
and 2 MBytes. Therefore, Bits 0 to 7 and Bits 22 to 31 of the PAGEx_RANGE register remain unchanged at a value of 0
even if a value of 1 is entered. If no bit at all is set in one of the PAGE RANGE registers, the range of this page is set to
256 bytes, by default. If several bits are set to 1 in one of the PAGE RANGE registers, the range is always calculated
based on the most significant bit (see Example 2 in the table below).
PAGEx_RANGE_HIGH PAGEx_RANGE_LOW Size of Page x
31 2423 16 15 8 7 0
00000000 00010000 01000000 00000000 1 Mbyte
00000000 00000110 00000000 00000000 256 Kbytes
00000000 00000010 00000000 00000000 128 Kbytes
00000000 00000000 00000001 00000000 256 bytes
Table 20: Setting of Various Page Sizes
The largest page determines the number of addresses that have to be connected to the LBU. In the page range table
above, the largest page is 1 Mbyte (i = Bit 20). The maximum addresses are calculated from Amax = 20 – 1. In this case,
address cables A [19:0] are required.
This addressing mechanism results in a mirroring of the specified page size in the total segment.
7.2 Page Offset Setting
The page offset of each page is set in the PAGEx_OFFSET_HIGH and PAGEx_OFFSET_LOW range registers (x = 0 to
3). Together, the two page offset registers yield a 32-bit address register. The register is evaluated in such a way that
the offset is evaluated only up to the highest set bit of the associated page range register. These bits are then switched
to the AHB bus as the highest address. The following table shows some examples for an offset calculation.
PAGEx_ OFFSET _HIGH PAGEx_ OFFSET _LOW Offset for Page x
31 2423 16 15 8 7 0
01000000 00000000 00000000 00000000 1 Gbyte
00010000 00000000 00000000 00000000 256 Mbytes
00000000 00000001 00000000 00000000 64 Kbytes
00000000 00000000 00000001 00000000 256 bytes
Table 21: Setting of Various Offset Areas
Because the host computer can always access the page registers, the pages can be reassigned at any time This is
useful, for example, if a page is to be used to initialize the I/O. If access to this address area is no longer required after
the initialization, the page can then be reassigned in order to access other address areas of the ERTEC 200.
Copyright © Siemens AG 2007. All rights reserved. 76 ERTEC 200 Manual
Technical data subject to change Version 1.1.0