HD66420 Datasheet, PDF (34/52 Pages) Hitachi Semiconductor – (RAM-Provided 160 Channel 4-Level Grey Scale Driver for Dot Matrix Graphics LCD)

HD66420
Power Down Modes
The HD66420 has a standby function providing low power-dissipation, which is initiated by internal
register settings. During standby mode, all the HD66420 functions are inactive and data in the display
RAM and internal registers except the DISP bit are retained. However, only control registers can be
accessed during standby mode. HD66420 has an another power down mode: partial display. In this mode
only a part of display is active. However, this duty ratio is 1/8 so the external power supply for LCD drive
will be inactive. The oscillator does not halt, thus dissipating more power than standby mode. Table 7 lists
the LCD driver output pin status during standby mode. Figure 20 shows the procedure for initiating and
canceling a standby mode and figure 21 shows the procedure for changing oscillator. Note that these
procedure must be strictly followed to protect data in the display RAM.
Table 7 Output Pin Status during Power Down modes
Signal Name
COM1–COM80
SEG1–SEG160
STBY
1
0
1
0
Status
Output VLCD (display off)
Output common signals (VLCD–GND)
Output VLCD (display off)
Output segment signals (VLCD–GND)
Set STBY bit to 1 (control register 1)
Oscillation halts
External power supply off
Initiation
Standby mode
Clear STBY and PWR bits to 0 (control register 1)
Oscillator starts
Internal operation starts
Wait for oscillation and external
power supply to stabilize
Cancellation
Set DISP bit to 1 (control register 1)
Display starts
Figure 20 Procedure for Initiation and Canceling a Standby Mode
34