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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.
assignment for all the data formats supported by the SSI module.
Format
31
30
8-bit lsb Aligned
8-bit msb Aligned
10-bit lsb Aligned
10-bit msb Aligned
12-bit lsb Aligned
12-bit msb Aligned
16-bit lsb Aligned
16-bit msb Aligned
15 14 13 12 11 10
18-bit lsb Aligned
18-bit msb Aligned
17 16 15 14 13 12 11 10
20-bit lsb Aligned
20-bit msb Aligned
19 18 17 16 15 14 13 12 11 10
22-bit lsb Aligned
22-bit msb Aligned
21 20 19 18 17 16 15 14 13 12 11 10
24-bit lsb Aligned
24-bit msb Aligned
23 22 21 20 19 18 17 16 15 14 13 12 11 10
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).
Freescale Semiconductor
Table 25-24. Data Alignment
29
28
27
26
25
24
23
22
9
8
7
6
9
8
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
MCF52277 Reference Manual, Rev. 1
Bit Number
21
20
19
18
17
16
15
14
7
6
9
8
11 10
15 14 13 12 11 10 9
5
4
3
2
1
0
17 16 15 14 13 12 11 10 9
7
6
5
4
3
2
1
0
19 18 17 16 15 14 13 12 11 10 9
9
8
7
6
5
4
3
2
21 20 19 18 17 16 15 14 13 12 11 10 9
9
8
7
6
5
4
9
8
7
6
Synchronous Serial Interface (SSI)
Table 25-24
shows the bit
13
12
11
10
9
8
7
6
5
7
6
5
5
4
3
2
1
0
9
8
7
6
5
7
6
5
4
3
2
1
0
11 10 9
8
7
6
5
9
8
7
6
5
4
3
2
1
8
7
6
5
8
7
6
5
8
7
6
5
1
0
8
7
6
5
3
2
1
0
8
7
6
5
5
4
3
2
1
0
4
3
2
1
0
4
3
2
1
0
4
3
2
1
0
4
3
2
1
0
0
4
3
2
1
0
4
3
2
1
0
4
3
2
1
0
4
3
2
1
0
4
3
2
1
0
25-47
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