LM8322EVALKIT National Semiconductor, LM8322EVALKIT Datasheet - Page 14

• Manufacturer Part Number: LM8322EVALKIT
• Description: BOARD EVALUATION LM8322
• Manufacturer: National Semiconductor

Specifications of LM8322EVALKIT

• Main Purpose: Interface, Special Purpose
• Embedded: No
• Utilized Ic / Part: LM8322
• Primary Attributes: Mobile I/O Companion with Key-Scan, I/O Expansion, PWM, Access.bus Host
• Secondary Attributes: Board has MCU for USB to PC GUI
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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12.0 Keypad Interface
12.1 EVENT CODE ASSIGNMENT
After power-on reset and host initialization, the LM8322 starts
scanning the keypad. It stays active for a default time of about
500 ms after the last key is released, after which it enters Halt
The codes are loaded into the FIFO buffer in the order in
which they occurred. Table 6 shows an example sequence of
12.2 KEYPAD SCAN CYCLES
The LM8322 starts new scan cycles at fixed time intervals of
about 4 milliseconds. If a change in the state of the keypad is
detected, the keypad is rescanned after a debounce delay.
When the state change has been reliably captured, it is en-
coded and written to the FIFO buffer.
Figure 8 shows the relationship between a KP-Yx output and
a KP-Xx input over multiple scan cycles during a key press
event. Between scan cycles, the KP-Yx outputs that are spec-
ified by the SET_KEY_SIZE command (0x90) for keypad
scanning are driven low.
KP-X0
KP-X1
KP-X2
KP-X3
KP-X4
KP-X5
KP-X6
KP-X7
Event Number
1
2
3
4
5
6
7
8
KP-Y0 KP-Y1 KP-Y2 KP-Y3 KP-Y4 KP-Y5 KP-Y6 KP-Y7 KP-Y8 KP-Y9 KP-Y10 KP-Y11 SF Keys
0x01
0x11
0x21
0x31
0x41
0x51
0x61
0x71
0x02
0x12
0x22
0x32
0x42
0x52
0x62
0x72
Event Code
0xC5
0xB2
0x5F
0x45
0x32
0x81
0x01
0x00
0x03
0x13
0x23
0x33
0x43
0x53
0x63
0x73
FIGURE 7. Example Event Codes Loaded in FIFO Buffer
0x04
0x14
0x24
0x34
0x44
0x54
0x64
0x74
TABLE 5. Keypad Matrix Code Assignments
TABLE 6. Example Sequence of Events
Event on Input
0x05
0x15
0x25
0x35
0x45
0x55
0x65
0x75
KP-X4
KP-X3
KP-X4
KP-X3
KP-X0
KP-X5
KP-X0
n.a.
0x06
0x16
0x26
0x36
0x46
0x56
0x66
0x76
14
0x07
0x17
0x27
0x37
0x47
0x57
0x67
0x77
mode to minimize power consumption (typically <5 µA stand-
by current).
Table 5 lists the codes assigned to the matrix positions en-
coded by the hardware. Key-press events are assigned the
codes listed in Table 5 , but with the MSB set. When a key is
released, the MSB of the code is clear.
events, and Figure 7 shows the resulting sequence of event
codes loaded into the FIFO buffer.
Driven Output
0x08
0x18
0x28
0x38
0x48
0x58
0x68
0x78
KP-Y4
KP-Y1
KP-Y4
KP-Y1
KP-Y0
KP-Y0
n.a.
n.a.
0x09
0x19
0x29
0x39
0x49
0x59
0x69
0x79
FIGURE 8. Keypad Scan Cycles
Key is pressed
Key is pressed
Key is released
Key is released
Key is pressed
SF Key is released
Key is released
Indicates end of stored events
0x0A
0x1A
0x2A
0x3A
0x4A
0x5A
0x6A
0x7A
30013607
0x0B
0x1B
0x2B
0x3B
0x4B
0x5B
0x6B
0x7B
Description
0x0C
0x1C
0x2C
0x3C
0x4C
0x5C
0x6C
0x7C
0x0F
0x1F
0x2F
0x3F
0x4F
0x5F
0x6F
0x7F
30013608