From d4478de9546e9c4dddd4c8dd6a8fb9429ec2087b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?King=20K=C3=A9vin?= <kingkevin@cuvoodoo.info>
Date: Sat, 9 Jul 2022 13:44:53 +0200
Subject: [PATCH] doc: add project documentation

---
 README.md | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index bb750e7..d49b11e 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,24 @@
-firmware template for ST STM8S micro-controller.
-includes register definitions using macros and structures.
+STM8S003 firmware for the [I²C to HD44780 adapter](https://git.cuvoodoo.info/kingkevin/board/src/branch/i2c_hd44780).
+
+I²C commands (first byte).
+
+simplified commands:
+
+- 0x0 INIT: initialize LCD, as 2-line, 5x8 dots, no blinking or cursor
+- 0x1 LINE1: write to line 1, followed by ASCII text
+- 0x2 LINE2: write to line 2, followed by ASCII text
+- 0x3 DISPLAY_ON: turn display on
+- 0x4 DISPLAY_OFF: turn display off
+- 0x5 BRIGHTNESS: set backlight brightness, followed by 0-255 value
+
+raw instructions, directly mapping to HD44780, followed by instruction byte or data bytes if applicable:
+
+- 0x6 CLEAR_DISPLAY
+- 0x7 RETURN_HOME
+- 0x8 ENTRY_MODE_SET
+- 0x9 DISPLAY
+- 0xa CURSOR_DISPLAY_SHIFT
+- 0xb FUNCTION_SET
+- 0xc CGRAM_ADDR
+- 0xd DDRAM_ADDR
+- 0xe DATA