HD44780U
Reset Function
Initializing by Internal Reset Circuit
An internal reset circuit automatically initializes the HD44780U when the power is turned on. The
following instructions are executed during the initialization. The busy flag (BF) is kept in the busy state
until the initialization ends (BF = 1). The busy state lasts for 10 ms after VCC rises to 4.5 V.
1. Display clear
2. Function set:
DL = 1; 8-bit interface data
N = 0; 1-line display
F = 0; 5 × 8 dot character font
3. Display on/off control:
D = 0; Display off
C = 0; Cursor off
B = 0; Blinking off
4. Entry mode set:
I/D = 1; Increment by 1
S = 0; No shift
Note: If the electrical characteristics conditions listed under the table Power Supply Conditions Using
Internal Reset Circuit are not met, the internal reset circuit will not operate normally and will fail to
initialize the HD44780U. For such a case, initial-ization must be performed by the MPU as
explained in the section, Initializing by Instruction.
Instructions
Outline
Only the instruction register (IR) and the data register (DR) of the HD44780U can be controlled by the
MPU. Before starting the internal operation of the HD44780U, control information is temporarily stored
into these registers to allow interfacing with various MPUs, which operate at different speeds, or various
peripheral control devices. The internal operation of the HD44780U is determined by signals sent from the
MPU. These signals, which include register selection signal (RS), read/
write signal (R/W), and the data bus (DB0 to DB7), make up the HD44780U instructions (Table 6). There
are four categories of instructions that:
•
•
•
•
Designate HD44780U functions, such as display format, data length, etc.
Set internal RAM addresses
Perform data transfer with internal RAM
Perform miscellaneous functions
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HITACHI [ HITACHI SEMICONDUCTOR ]
