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Synchronous Serial Interface (SSI)
Freescale Semiconductor
27-51
The supported data formats are:
•
msb alignment
•
lsb alignment
— Zero-extended (receive data only)
— Sign-extended (receive data only)
With msb alignment, the most significant byte is bits 31–24 of the data register if the word length is larger
than, or equal to, 16 bits. If the word length is less than 16 bits and msb alignment is chosen, the most
significant byte is bits 15–8. With lsb alignment, the least significant byte is bits 7–0. The
SSI_TCR[TXBIT0] and the SSI_RCR[RXBIT0] bits control data alignment.
shows the bit
assignment for all the data formats supported by the SSI module.
In addition, if lsb alignment is selected, the receive data can be zero-extended or sign-extended.
•
In zero-extension, all bits above the most significant bit are 0s. This format is useful when data is
stored in a pure integer format.
•
In sign-extension, all bits above the most significant bit are equal to the most significant bit. This
format is useful when data is stored in a fixed-point integer format (which implies fractional
values).
Table 27-28. Data Alignment
Format
Bit Number
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
8-bit lsb Aligned
7
6
5
4
3
2
1
0
8-bit msb Aligned
7
6
5
4
3
2
1
0
10-bit lsb Aligned
9
8
7
6
5
4
3
2
1
0
10-bit msb Aligned
9
8
7
6
5
4
3
2
1
0
12-bit lsb Aligned
11 10
9
8
7
6
5
4
3
2
1
0
12-bit msb Aligned
11 10
9
8
7
6
5
4
3
2
1
0
16-bit lsb Aligned
15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
16-bit msb Aligned
15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
18-bit lsb Aligned
17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
18-bit msb Aligned
17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
20-bit lsb Aligned
19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
20-bit msb Aligned
19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
22-bit lsb Aligned
21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
22-bit msb Aligned
21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
24-bit lsb Aligned
23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
24-bit msb Aligned
23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Содержание MCF54455
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