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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 3).
PAGEx_RANGE_HIGH
31
2423
00000000 00000000
00000000 00010000
00000000 00000110
00000000 00000010
Table 19: 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
31
2423
00000000 00000000
01000000 00000000
00010000 00000000
00000000 00000001
Table 20: 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 400.
Copyright © Siemens AG 2010. All rights reserved.
Technical data subject to change
PAGEx_RANGE_LOW
16
15
8 7
00000001 00000000
01000000 00000000
00000000 00000000
00000000 00000000
PAGEx_ OFFSET _LOW
16
15
8 7
00000001 00000000
00000000 00000000
00000000 00000000
00000000 00000000
Size of pagex
0
256 bytes
1 Mbytes
256 Kbytes
128 Kbytes
Offset for Pagex
0
256 bytes
1 Gbyte
256 Mbytes
64 Kbytes
Page
75
ERTEC 400 Manual
Version 1.2.2
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