HD66727 Datasheet, PDF (51/97 Pages) Hitachi Semiconductor – Low-Power Dot-Matrix Liquid Crystal Display Controller/Driver with Key Scan Function

HD66727
Key Scan Control
Key Scan Mechanism
The key matrix scanner senses and holds the key states at each rising edge of the key strobe signals (KST)
that are output by the HD66727. The key strobe signals are output as time-multiplexed signals from KST0
to KST7. After passing through the key matrix, these strobe signals are used to sample the key state on four
inputs KIN0 to KIN3, enabling up to 32 keys to be scanned (Figure 25).
The states of inputs KIN0 to KIN3 are sampled by key strobe signal KST0 and latched into the SCAN0
register. Similarly, the data sampled by strobe signals KST1 to KST7 is latched into the SCAN1 to SCAN7
registers, respectively (Figure 26). Key pressing is stored as 1 in these registers.
The generation cycle and pulse width of the key strobe signals depend on the operating frequency
(oscillation frequency) of the HD66727, the display line determined by the NL1 bit, and the key scan cycle
determined by the KF0 and KF1 bits. For example, when the operating frequency is 160 kHz, NL1 is 1,
and KF0 and KF1 are both 0, the generation cycle is 8.0 ms and the pulse width is 1.0 ms (Figure 27).
When the operating frequency (oscillation frequency) is changed, the above generation cycle and the pulse
width are also changed in inverse proportion (Table 28).
Key matrix
Detail
D03 D02 D01 D00
D13 D12 D11 D10
D23 D22 D21 D20
D33 D32 D31 D30
D43 D42 D41 D40
D53 D52 D51 D50
D63 D62 D61 D60
D73 D72 D71 D70
KST0
KST1
KST2
KST3
KST4
KST5
KST6
KST7
KIN0
KIN1
KIN2
KIN3
Key state input
Key strobe
HD66727
Figure 25 Key Scan Configuration
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