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HD-44780 LCD Information

This app note describes the commands that control an HD-44780-based LCD display.

LCD Commands

b7 b6 b5 b4 b3 b2 b1 b0 Description
0 0 0 0 0 0 0 1 Clear the display. Set address to 0.
0 0 0 0 0 0 1 - Return to home position.
0 0 0 0 0 1 d s Entry mode.
d = 0 (positive direction), 1 (negative direction)
s = 0 (no shift), 1 (shift)
0 0 0 0 1 d b c Display⁄cursor enable
d = 0 (display off), 1 (display on)
b = 0 (blink off), 1 (blink on)
c = 0 (cursor off), 1 (cursor on)
0 0 0 1 s r - - Display⁄ cursor shift
s = 0 (cursor shift only), 1 (display and cursor shift)
r = 0 (right), 1 (left)
0 0 1 d n f - - Data interface
d = 0 (8 bit), 1 (4 bit)
n = 1 (2 lines), 0 (1 line)
f = 1 (5*10 dots), 0 (5*8 dots)
  1 a a a a a a Set CG RAM address
1 a a a a a a a Set DD RAM address


Instruction Description (From Hitachi)

Clear Display

Clear display writes space code 20H (character pattern for character code 20H must be a blank pattern) into all DDRAM addresses. It then sets DDRAM address 0 into the address counter, and returns the display to its original status if it was shifted. In other words, the display disappears and the cursor or blinking goes to the left edge of the display (in the first line if 2 lines are displayed). It also sets I⁄D to 1 (increment mode) in entry mode. S of entry mode does not change.

Return Home

Return home sets DDRAM address 0 into the address counter, and returns the display to its original status if it was shifted. The DDRAM contents do not change. The cursor or blinking go to the left edge of the display (in the first line if 2 lines are displayed).

Entry Mode Set

I⁄D: Increments (I⁄D = 1) or decrements (I⁄D = 0) the DDRAM address by 1 when a character code is written into or read from DDRAM. The cursor or blinking moves to the right when incremented by 1 and to the left when decremented by 1. The same applies to writing and reading of CGRAM.

S: Shifts the entire display either to the right (I⁄D = 0) or to the left (I⁄D = 1) when S is 1. The display does not shift if S is 0. If S is 1, it will seem as if the cursor does not move but the display does. The display does not shift when reading from DDRAM. Also, writing into or reading out from CGRAM does not shift the display.

Display On⁄Off Control

D: The display is on when D is 1 and off when D is 0. When off, the display data remains in DDRAM, but can be displayed instantly by setting D to 1.

C: The cursor is displayed when C is 1 and not displayed when C is 0. Even if the cursor disappears, the function of I⁄D or other specifications will not change during display data write. The cursor is displayed using 5 dots in the 8th line for 5 ´ 8 dot character font selection and in the 11th line for the 5 ´ 10 dot character font selection (Figure 13).

B: The character indicated by the cursor blinks when B is 1 (Figure 13). The blinking is displayed as switching between all blank dots and displayed characters at a speed of 409.6-ms intervals when fcp or fOSC is 250 kHz. The cursor and blinking can be set to display simultaneously. (The blinking frequency changes according to fOSC or the reciprocal of fcp. For example, when fcp is 270 kHz, 409.6 ´ 250⁄270 = 379.2 ms.)

Cursor or Display Shift

Cursor or display shift shifts the cursor position or display to the right or left without writing or reading display data (Table 7). This function is used to correct or search the display. In a 2-line display, the cursor moves to the second line when it passes the 40th digit of the first line. Note that the first and second line displays will shift at the same time. When the displayed data is shifted repeatedly each line moves only horizontally. The second line display does not shift into the first line position. The address counter (AC) contents will not change if the only action performed is a display shift.

Function Set

DL: Sets the interface data length. Data is sent or received in 8-bit lengths (DB7 to DB0) when DL is 1, and in 4-bit lengths (DB7 to DB4) when DL is 0.When 4-bit length is selected, data must be sent or received twice.

N: Sets the number of display lines.

F: Sets the character font.

Note: Perform the function at the head of the program before executing any instructions (except for the read busy flag and address instruction). From this point, the function set instruction cannot be executed unless the interface data length is changed.

Set CGRAM Address

Set CGRAM address sets the CGRAM address binary AAAAAA into the address counter. Data is then written to or read from the MPU for CGRAM.

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