Arduino: How to control a HD44780 based character LCD

Many characters LCD displays use so called HD44780 based protocol on interface. This is more like standard but i recommend to check datasheet from vendor. There can be small modifications and/or difference in timing. Especially timing is important. If communication rate is too quick, then LCD drop data or misbehave depending on internal state. I recommend to check busy flag if possible. If not then correct delay should be applied between commands. Result of commands can be checked via LCD Simulator prior to programing MCU. For example i like this one: DjLCDSIM.

Command Set

Clear Display

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
0	0		0	0	0	0	0	0	0	1		~ 1.52 ms

• Clear display data by writing 0x20 ("space") to whole DDRAM memory
• Set AC to DDRAM and 0x00
• Set entry mode to increment (I/D = 1)

Return Home

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
0	0		0	0	0	0	0	0	1	x		~ 1.52 ms

• Set AC to DDRAM and 0x00
• Return cursor and display to home (original) postition

Entry Mode Set

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
0	0		0	0	0	0	0	1	I/D	SH		~ 38 us

• Set the moving diresction of cursor and display
• I/D = Increment / Decrement DDRAM address
  • I/D = 1, cursor moves to right and DDRAM is increased by 1
  • I/D = 0, cursor moves to left and DRAM is decreased by 1
• SH = Shift (scroll) of entire display
  • SH = 1, after DDRAM write operation entire display is shifted (scrolled) according to I/D value
  • SH = 0, no shifting (scrolling) is performed

Display ON / OFF Control

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
0	0		0	0	0	0	1	D	C	B		~ 38 us

Cursor or Display Shift

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
0	0		0	0	0	1	S/C	R/L	x	x		~ 38 us

Function set

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
0	0		0	0	1	DL	N	F	x	x		~ 38 us

Set CGRAM Address

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
0	0		0	1	AC5	AC4	AC3	AC2	AC1	AC0		~ 38 us

Set DDRAM Address

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
0	0		1	AC6	AC5	AC4	AC3	AC2	AC1	AC0		~ 38 ms

Read Busy Flag and Address

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
0	1		BF	AC6	AC5	AC4	AC3	AC2	AC1	AC0		~ 0 us

Write data to RAM

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
1	0		D7	D6	D5	D4	D3	D2	D1	D0		~ 38 us

Read data from RAM

RS	R/W		DB7	DB6	DB5	DB4	DB3	DB2	DB1	DB0		Execution Time
1	1		D7	D6	D5	D4	D3	D2	D1	D0		~ 38 us