HD66727 Datasheet, PDF (55/97 Pages) Hitachi Semiconductor – Low-Power Dot-Matrix Liquid Crystal Display Controller/Driver with Key Scan Function

HD66727
Key Scan Interrupt (Wake-Up Function)
If the interrupt enable bit (IRE) is set to 1, the HD66727 sends an interrupt signal to the MPU on detecting
that a key has been pressed in the key scan circuit by setting the IRQ* output pin to a low level. An
interrupt signal can be generated by pressing any key in a 32-key matrix. The interrupt level continues to be
output during the key scan cycle in which the key is being pressed. See Figure 29.
Normal key scanning is performed and interrupts can occur in the HD66727 sleep mode (SLP = 1).
Accordingly, power consumption can be minimized in the sleep mode, where only annunciators can be
displayed, by triggering the MPU to read key states via the interrupt generated only when the HD66727
detects a key input from the 32-key matrix. For details, refer to the Sleep Mode section.
On the other hand, normal key scanning and the internal operating clock are halted in the standby mode
(STB = 1). During this period, the KST0 output is kept low, so the HD66727 can always sense four key
inputs D00 to D03, connected with KIN0 to KIN3, respectively. Therefore, if any of the four keys is
pressed in the standby mode, an interrupt occurs. Accordingly, power consumption can be further
minimized in the standby mode, where the whole system is inactive, by triggering the MPU via the
interrupt generated only when the HD66727 detects a key input from the above four keys. Note that the
interrupt generated in the standby mode automatically starts internal R-C oscillation. For details, refer to
the Standby Mode section.
The IRQ* output pin is pulled up to the V_CC with an internal MOS resistor of approximately 50 kΩ;
additional external resistors may be required to obtain stronger pull-ups. Interrupts may occur if noise
occurs in KIN input during key scanning. Interrupts must be inhibited if not needed by setting the interrupt
enable bit (IRE) to 0.
Figure 30 shows key scan interrupt processing flow in sleep and standby modes.
V_CC
HD66727
IRQ*
MPU
IRQ*
Interrupt generated
Figure 29 Interrupt Generation
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