hd66421 Renesas Electronics Corporation., hd66421 Datasheet - Page 30

• Manufacturer Part Number: hd66421
• Description: Ram-provided 160 Channel 4-level Grey Scale Driver For Dot Matrix Graphics Lcd
• Manufacturer: Renesas Electronics Corporation.

Power Down Modes
The HD66421 has a standby function providing
low power-dissipation, which is initiated by
internal register settings. During standby mode,
all the HD66421 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.
HD66421 has an another power down mode:
partial display. In this mode only a part of display
Preliminary
Table 7 Output Pin Status during Power Down modes
SEG1-SEG160
Signal Name
COM1-COM100
Clear STBY and PWR bits to 0 and AMP bit to 1
Figure 27 Procedure for Initiation and Canceling a Standby Mode
Set DTY or GRAY bit to 1 (control register 2)
Set STBY bit to 1 and AMP bit to 0
Set DISP bit to 1 (control register 1)
Wait for oscillation and external
power supply to stabilize
Clear HOLT bit to 0 (control register 1)
Set HOLT bit to 1 (control register 1)
Figure 28 Procedure for Changing Oscillator
Wait for oscillation to stabilize
(control register 1)
(control register 1)
Standby mode
STBY
1
0
1
0
Output VLCD (display off)
Output common signals (VLCD - GND)
Output VLCD (display off)
Output segment signals (VLCD - GND)
30
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
6 lists the LCD driver output pin status during
standby mode. Figure 27 shows the procedure for
initiating and canceling a standby mode and
figure 28 shows the procedure for changing
oscillator. Note that these procedure must be
strictly followed to protect data in the display
RAM.
Status
Oscillator starts
OP amp power on
Internal operation starts
Oscillation halts
OP amp power off
External power supply off
Display starts
Internal operation stops
Oscillator 2 starts working
Internal operation starts
Rev. 1.1E '99.02.10
Cancellation
Initiation
HD66421