HD44780 datasheet(23/59 Pages) HITACHI

部品番号	HD44780

部品情報	Dot Matrix Liquid Crystal Display Controller/Driver

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メーカー	HITACHI [Hitachi Semiconductor]

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HD44780U

23

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 V

CC 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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