
HD66726
53
Reset Function
The HD66726 is internally initialized by RESET input. During initialization, the system executes a clear
display instruction after reset is canceled. The system executes the other instructions during the reset
period. Because the busy flag (BF) indicates a busy state (BF = 1) during the reset period and the clear
display instruction is executed following reset cancellation, no instruction or RAM data access from the
MPU is accepted. The reset input must be held for at least 1 ms. Any initializing instruction must wait for
1000 clock cycles after the reset is canceled so that execution of the clear display instruction can be
completed.
Instruction Set Initialization:
1. Clear display executed (Writes 20H to DDRAM)
2. Return home executed (Sets the address counter (AC) to 00H to select DDRAM)
3. Start oscillation executed
4. Driver output control (SGS = 0, CMS = 0)
5. Power control (AMP = 0: LCD power off, SLP = 0: Sleep mode off, STB = 0: Standby mode off)
6. Single boost (BT1/0 = 00), 1/8 bias drive (BS2/1/0 = 000), Weak contrast (CT4-0 = 00000)
7. Entry mode set (REV = 0: Normal display, I/D = 1: Increment by 1, GR = 0: Character display mode)
8. Cursor display off (B/W = 0, C = 0, B = 0)
9. Display on/off control (D = 0: Display off, CEN = 0: Normal position, LC = 0: Line-cursor off)
10.Display line control (NL2/1/0 = 100: 1/34 duty ratio)
11.Double-height display off (DL3/2/1 = 000)
l2. Vertical scroll control (SN2/1/0 = 000: First line displayed at the top, SL2/1/0: First raster-row
displayed at the top of the first line)
13.CGROM memory bank 0 selection (RL5/4/3/2/1 = 00000)
14.Key scan control (IRE = 0: Key scan interrupt (IRQ) generation disabled, KF1/0 = 00: Key scan set to
32 cycles)
15. Port control (PT2/1/0 = 000: PORT2/1/0 output = GND level)
RAM Data Initialization:
1. DDRAM
All addresses are initialized to 20H by the clear display instruction after the reset is canceled.
2. CGRAM/SEGRAM
This is not automatically initialized by reset input but must be initialized by software while display is
off (D = 0).
Output Pin Initialization:
1. LCD driver output pins (SEG/COM): Outputs GND level
2. Booster output pins (VLOUT): Outputs GND level
3. Oscillator output pin (OSC2): Outputs oscillation signal
4. Key strobe pins (KST0 to KST3): Output strobe signals at specified time intervals
5. Key scan interrupt pin (IRQ*): Outputs V
CC
level