Freescale Semiconductor MPC5553, Справочное руководство

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MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
18-6 Freescale Semiconductor
The host can also access the SDM space mirrored in an alternate area with parameter sign extension (PSE).
PSE allows for 24-bit data to be accessed as 32 bit sign-extended data without using the
MPC5553/MPC5554’s bandwidth to extend the data.
Parameter signal extension accesses differ from the usual host accesses to the original SDM area as
follows:
• Writes are effective only to the lower 3 bytes of a word: the word’s most significant byte (byte
address) is kept unaltered in SDM.
Figure 18-3. SDM PSE Area Write
NOTE
For the most significant byte, it should be recalled that the word format is
big endian, as in the default Power Architecture embedded category word
format.
• Reads return the lower 3 bytes of a word sign-extended to 32 bits, that is: the most significant bit
of the word’s second most significant byte (byte addresses) is copied in all 8 bits of the most
significant read byte.
Figure 18-4. PSE Accesses
Each eTPU channel can be associated with a variable number of parameters located in the SDM, according
to its selected function. In addition, the SDM can be fully shared between two eTPU engines, enabling
communication between them. Each function may require a different number of parameters. During eTPU
initialization the host has to program channel base addresses, allocating proper parameters for each
channel according to its selected function.
[31:24] [23:16] [15:8] [7:0]
Write 24 bit data
SDM
[31:24] [23:16] [15:8] [7:0]
SDM
0 0 1 0 1 1 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 1
0 0 1 0 1 1 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 1 0 0 0 0 0 0 0 0
Example 1:
Read with
sign extension
[31:24] [23:16] [15:8] [7:0]
SDM
1 0 1 0 1 1 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 1
1 0 1 0 1 1 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1
Example 2:
Read with
sign extension