HD66727 Datasheet, PDF (86/97 Pages) Hitachi Semiconductor – Low-Power Dot-Matrix Liquid Crystal Display Controller/Driver with Key Scan Function

HD66727
Standby Mode
Setting the standby mode bit (STB) to 1 puts the HD66727 in the standby mode, where the device stops
completely, halting all internal operations including the R-C oscillator, thus further reducing current
consumption compared to that in the sleep mode. Specifically, character and segment displays, which are
controlled by the multiplexing drive method, are completely halted. Here, all the SEG (SEG1 to SEG60)
and COM (COM1 to COM34) pins output the V_CC level, resulting in no display. If the AMP bit is set to 0
in the standby mode, the LCD drive power supply can be turned off.
Annunciators can be displayed simply by supplying an approximately 40-Hz alternating signal for the LCD
drive signals to the EXM pin externally. If annunciator display is unnecessary during the standby mode, the
EXM pin must be fixed to the V_CC or GND level and the annunciator display on bit (DA) set to 0.
During the standby mode, no instructions can be accepted other than those for annunciator display, the
start-oscillator instruction, and the key scan interrupt generation enable instruction. To cancel the standby
mode, issue the start oscillator instruction to stabilize R-C oscillation before setting the STB bit to 0.
Although key scan is halted in the standby mode, the HD66727 can detect four key inputs connected with
strobe signal KST0, thus generating the key scan interrupt (IRQ*). This means, the system can be activated
from the completely inactive state. For details, refer to the Key Scan Control section.
Figure 50 shows the procedure for setting and canceling the standby mode.
Turn off the LCD power supply: AMP = 0
Set standby mode: STB = 1
Supply an external alternating signal to the EXM pin
Standby mode (only annunciator display is available)
Issue the start-oscillator instruction
Wait at least 10 ms
Cancel standby mode: STB = 0
Turn on the LCD drive power supply: AMP = 1
Only for annunciator display;
set the DA bit to 0 when
annunciator display is not necessary.
Figure 50 Procedure for Setting and Canceling Standby Mode
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