Key Scan Operation

1. Key Scan Timing

The key scan period is 375T [s]. The key scan is performed twice to reliably determine the key on/off states, and the

LSI detects key data agreement. When the key data agrees, the LSI determines that a key has been pressed, and outputs

a key read request (by setting DO low) 800T [s] after the key scan started. If a key is pressed again without the key data

agreeing, a key scan is performed once more. Thus key on/off operations shorter than 800T [s] cannot be detected.

*1 The high or low states of these signals in sleep mode are determined by the S0 and S1 control data bits.

2. Key Scan during Normal Mode

• The pins KS1 to KS6 are set high.

• A key scan starts if any key is pressed, and the scan continues until all keys have been released. Multiple key

presses can be recognized by determining if multiple key data bits have been set.

• When a key has been pressed for 800T [s] (where T = 1/f

is output to the controller. The controller acknowledges this request and reads the key data. However, DO will go

high when CE is high during a serial data transfer.

• After the controller has finished reading the key data, the LSI clears the key data read request (by setting DO high)

and performs another key scan. Note that since DO is an open drain output, a pull-up resistor of between 1 and 10 k

Ω

is required.

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LC75852E, 75852W