Ameba-D User Manual
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318
16.2.3
FIFO Mechanism
The FIFO with depth of 16 and width of 12-bit is used to store key press and release events, as shown in Fig 16-6.
12-bit FIFO with depth of 16
DATA0
DATA1
DATA14
7
6
5
4
3
2
1
0
8
DATA15
New Data
Column Index
Row Index
Event
9
10
11
Fig 16-6 FIFO structure
In the FIFO item, bit[7:0] indicates the key # pressed or released in a keypad array. Bit[8] indicates a key press or release event happened. A ‘0’
means a key release event. A ‘1’ means that a key has been pressed (which can be cleared on a read). When FIFO is full and another item is
pushed into the FIFO, an overflow interrupt is triggered. When FIFO is empty and is read, an overread interrupt is triggered.
The key value assignment is listed in Table 16-1.
Table 16-1 Key value assignment
Column
Row
0
1
2
3
4
5
6
7
0
11
12
13
14
15
16
17
18
1
21
22
23
24
25
26
27
28
2
31
32
33
34
35
36
37
38
3
41
42
43
44
45
46
47
48
4
51
52
53
54
55
56
57
58
5
61
62
63
64
65
66
67
68
6
71
72
73
74
75
76
77
78
7
81
82
83
84
85
86
87
88
16.2.4
Clock Configuration
There are two clock domains in the Key-Scan design, as shown in Fig 16-7.
The green part works in low power clock domain, which clock isn’t gated in low power modes.
The blue part works under bus clock domain (10M), it is gated in low power modes. In bus clock domain, some of the logic works in
scan_clk frequency, which is divided from bus clock.
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