projects / sigrok-dumps.git / blame
| Commit | Line | Data |
|---|---|---|
| 3093302b GS |
1 | ------------------------------------------------------------------------------- |
| 2 | Hitachi HD44780 display controller, 4-bit mode, initialization sequence | |
| 3 | ------------------------------------------------------------------------------- | |
| 4 | ||
| 5 | This capture contains the initialization sequence of an Hitachi HD44780 | |
| 6 | display controller which is very popular for 2x16, 4x20, and similar | |
| 7 | character oriented display modules. | |
| 8 | ||
| 9 | The specific hardware setup that got recorded uses 4-bit mode, which | |
| 10 | means that data gets communicated on lined D4-D7 only, and D0-D3 are | |
| 11 | not connected. | |
| 12 | ||
| 13 | ||
| 14 | Logic analyzer setup | |
| 15 | -------------------- | |
| 16 | ||
| 17 | The capture was taken with an ASIX Sigma2 logic analyzer, sampling 8 | |
| 18 | logic channels at a rate of 50MHz: | |
| 19 | ||
| 20 | Probe HD44780 | |
| 21 | ------------------- | |
| 22 | 1 IR (infrared remote control, idle, not HD44780 related) | |
| 23 | 2 RS (selects "commands" and "display data" mode) | |
| 24 | 3 RW (read/write, always low for write, fixed in HW) | |
| 25 | 4 E (enable, falling edge clocks data transfers) | |
| 26 | 5 D4 (data lines ...) | |
| 27 | 6 D5 | |
| 28 | 7 D6 | |
| 29 | 8 D7 | |
| 30 | ||
| 31 | ||
| 32 | Data | |
| 33 | ---- | |
| 34 | ||
| 35 | See https://en.wikipedia.org/wiki/Hitachi_HD44780_LCD_controller for a | |
| 36 | list of display controller commands, and especially the 'Mode Selection' | |
| 37 | section which discusses the synchronization phase. | |
| 38 | ||
| 39 | The sequence demonstrates the following steps: | |
| 40 | - Synchronize to the LCD controller, cope with it being in any arbitrary | |
| 41 | state from previous execution. | |
| 42 | - Configure the LCD controller hardware to 4-bit mode, clear the screen | |
| 43 | and setup other parameters. | |
| 44 | - Print two text labels: "Hello LCD" and "counter", start printing | |
| 45 | counter values. | |
| 46 | ||
| 47 | When a dedicated HD44780 decoder is not available, the 'parallel' decoder | |
| 48 | can extract the most basic information: Clock on E (falling edge), D4-D7 | |
| 49 | of the display corresponds to D0-D3 of the decoder (D4-D7 of the decoder | |
| 50 | are not connected). Words consist of 8 bits (span 2 bus cycles), and are | |
| 51 | in big endian format. |