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PT6555 Datasheet, PDF (14/28 Pages) Princeton Technology Corp – LCD Driver IC
PT6555
KEY SCAN OPERATION
KEY SCAN TIMING
PT6555-LQ scans the keys twice (reads the key data twice) and if the key data matches, this key is defined as
PRESSED (or ON). A key scan period is equivalent to 384T (s). 800T (s) after the key scan commences, PT6555-LQ
outputs a key data read request. If the key data from the does not match and a key was pressed at that point, the keys
are scanned again. It must be noted that PT6555-LQ cannot detect a key which is pressed shorter than 800T (s).
Notes:
1. T=1/fosc where fosc=oscillation frequency
2. The Sleep Mode, the state of these pins is determined by the control bits- S0 and S1. Key Scan signals are not outputted from pins that are set to
“LOW” Level.
3. Only PT6555-LQ has KS1~KS6 pins.
KEY SCAN OPERATING UNDER THE NORMAL MODE
Under the Normal Mode, the Key Scan Output Pins - KS1 to KS6 are set to HIGH. When a key is pressed, a key scan
operation commences. The keys are scanned until all keys are released. For multiple key press operation, a multiple key
press is valid only if multiple key data bits have set and verified by the key scan.
If a key is pressed longer than 800T(s), PT6555-LQ outputs a key read data request (DO is set to “LOW” level) to the
controller. The controller acknowledges the request and reads the key data. It must be noted that if CE is HIGH during a
serial data transfer, then DO is set to “HIGH”.
After the controller reads the key data, the key data request is cleared (DO is set to HIGH) and another key scan
operation is performed.
Notes:
1. T=1/fosc, where fosc is the oscillation frequency.
2. DO is an open - drain output and requires a pull-high resistor between 1KΩ to 10KΩ.
3. Only PT6555-LQ has the DO pin.
V1.1
14
August, 2009