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HD44780 Datasheet(PDF) 21 Page - Hitachi Semiconductor |
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HD44780 Datasheet(HTML) 21 Page - Hitachi Semiconductor |
21 / 59 page HD44780U 21 Timing Generation Circuit The timing generation circuit generates timing signals for the operation of internal circuits such as DDRAM, CGROM and CGRAM. RAM read timing for display and internal operation timing by MPU access are generated separately to avoid interfering with each other. Therefore, when writing data to DDRAM, for example, there will be no undesirable interferences, such as flickering, in areas other than the display area. Liquid Crystal Display Driver Circuit The liquid crystal display driver circuit consists of 16 common signal drivers and 40 segment signal drivers. When the character font and number of lines are selected by a program, the required common signal drivers automatically output drive waveforms, while the other common signal drivers continue to output non-selection waveforms. Sending serial data always starts at the display data character pattern corresponding to the last address of the display data RAM (DDRAM). Since serial data is latched when the display data character pattern corresponding to the starting address enters the internal shift register, the HD44780U drives from the head display. Cursor/Blink Control Circuit The cursor/blink control circuit generates the cursor or character blinking. The cursor or the blinking will appear with the digit located at the display data RAM (DDRAM) address set in the address counter (AC). For example (Figure 8), when the address counter is 08H, the cursor position is displayed at DDRAM address 08H. AC6 0 AC5 0 AC4 0 AC3 1 AC2 0 AC1 0 AC0 0 1 00 2 01 3 02 4 03 5 04 6 05 7 06 8 07 9 08 10 09 11 0A 1 00 40 2 01 41 3 02 42 4 03 43 5 04 44 6 05 45 7 06 46 8 07 47 9 08 48 10 09 49 11 0A 4A AC cursor position cursor position Display position DDRAM address (hexadecimal) Display position DDRAM address (hexadecimal) For a 1-line display For a 2-line display Note: The cursor or blinking appears when the address counter (AC) selects the character generator RAM (CGRAM). However, the cursor and blinking become meaningless. The cursor or blinking is displayed in the meaningless position when the AC is a CGRAM address. Figure 8 Cursor/Blink Display Example |
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