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-------------------------------------------------------------------------------
Hitachi HD44780 display controller, 4-bit mode, initialization sequence
-------------------------------------------------------------------------------
This capture contains the initialization sequence of an Hitachi HD44780
display controller which is very popular for 2x16, 4x20, and similar
character oriented display modules.
The specific hardware setup that got recorded uses 4-bit mode, which
means that data gets communicated on lined D4-D7 only, and D0-D3 are
not connected.
Logic analyzer setup
--------------------
The capture was taken with an ASIX Sigma2 logic analyzer, sampling 8
logic channels at a rate of 50MHz:
Probe HD44780
-------------------
1 IR (infrared remote control, idle, not HD44780 related)
2 RS (selects "commands" and "display data" mode)
3 RW (read/write, always low for write, fixed in HW)
4 E (enable, falling edge clocks data transfers)
5 D4 (data lines ...)
6 D5
7 D6
8 D7
Data
----
See https://en.wikipedia.org/wiki/Hitachi_HD44780_LCD_controller for a
list of display controller commands, and especially the 'Mode Selection'
section which discusses the synchronization phase.
The sequence demonstrates the following steps:
- Synchronize to the LCD controller, cope with it being in any arbitrary
state from previous execution.
- Configure the LCD controller hardware to 4-bit mode, clear the screen
and setup other parameters.
- Print two text labels: "Hello LCD" and "counter", start printing
counter values.
When a dedicated HD44780 decoder is not available, the 'parallel' decoder
can extract the most basic information: Clock on E (falling edge), D4-D7
of the display corresponds to D0-D3 of the decoder (D4-D7 of the decoder
are not connected). Words consist of 8 bits (span 2 bus cycles), and are
in big endian format.
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