LM8322 datasheet(16/42 Pages) NSC

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30013610

FIGURE 10. Keypad Interface Example

In the example above, three keys (Up, Down, and Select) are

connected as SF keys (connected directly to ground). Al-

though they could have shared the KP-Xx inputs used with

the scanned keys, the advantage of placing them on their own

KP-Xx inputs is that it allows scanning the keypad while an

SF key is pressed. If an SF key shares a KP-Xx input with any

scanned keys, pressing the SF key prevents the LM8322 from

reading the scanned keys.

The SET_KEY_SIZE command includes a data byte that

specifies the keypad size. The upper 4 bits of the data byte

specify the number of KP-Xx inputs, and the lower 4 bits

specify the number of KP-Yx outputs. The minimum number

of inputs and outputs is 3. Therefore, the minimum keypad

configuration supports 3 × 3 + 3 SF keys (total of 12 keys).

The maximum number of KP-Xx inputs is 8, and the maximum

number of KP-Yx pins is 12. All KP-Xx and KP-Yx pins not

used for the keyboard interface can be used for general-pur-

pose I/O.

For the example shown in Figure 10, the SET_KEY_SIZE

command would specify 8 KP-Xx inputs and 4 KP-Yx outputs.

13.0 General-Purpose I/O Ports

Any unused KP-Xx and KP-Yx pins may be used as general-

purpose I/O (GPIO) port pins. The WRITE_PORT_SEL

(0x85) command selects the port direction, in which a clear

bit in the parameter to the command selects the input direction

and a set bit selects the output direction.

The WRITE_PORT_STATE (0x86) command selects either

the

port

level

when

configured

output

(by

the

WRITE_PORT_SEL command) or when configured as an in-

put selects between a high-impedance input or an input with

a pullup or pulldown device. The selection between pullup or

pulldown devices is controlled by the parameter bytes to the

WRITE_PULL_DOWN (0x84) command. Clear bits in the pa-

rameter bytes select pullup devices, while set bits select

pulldown devices.

Table 7 shows the GPIO port configurations selected by the

bits in the WRITE_PORT_SEL, WRITE_PORT_STATE, and

WRITE_PULL_DOWN command parameters.

TABLE 7. GPIO Port Control Bits

WRITE_PORT_SEL

WRITE_PORT_STATE

WRITE_PULL_DOWN

Description

High-Impedance Input

Input with Pullup Device

Input with Pulldown Device

Output, Drive Low

Output, Drive High

Any pins used as GPIO ports must be configured after the

peripheral configuration has been initialized with the

WRITE_CFG command (0x81) and the keypad configuration

has been initialized with the SET_KEY_SIZE command

(0x90). The default keypad configuration after reset is a 3 × 3

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