HD44780 documentation (#262)

extras/hd44780/README.md

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+# HD44780 LCD display driver
+
+## Connection type
+
+Driver supports GPIO connections to module and I2C GPIO expanders as well.
+Define `HD44780_I2C = 0` in application makefile for direct GPIO connection.
+
+See `examples/i2c_lcd_test` and `examples/hd44780_test` .
+
+## Display types
+
+### 8x1
+
+#### Memory layout
+
+![0801 display](img/0801.png)
+
+#### Example
+
+```C
+hd44780_t lcd = {
+    .addr = ADDR,
+    .font = HD44780_FONT_5X8,
+    .lines = 1,
+    .pins = {
+        .rs = 0,
+        .e  = 2,
+        .d4 = 4,
+        .d5 = 5,
+        .d6 = 6,
+        .d7 = 7,
+        .bl = 3
+    },
+    .backlight = true
+};
+```
+
+### 16x1
+
+#### Memory layout
+
+![1601 display](img/1601.png)
+
+#### Example
+
+```C
+hd44780_t lcd = {
+    .addr = ADDR,
+    .font = HD44780_FONT_5X8,
+    .lines = 2,
+    .pins = {
+        .rs = 0,
+        .e  = 2,
+        .d4 = 4,
+        .d5 = 5,
+        .d6 = 6,
+        .d7 = 7,
+        .bl = 3
+    },
+    .backlight = true
+};
+hd44780_init(&lcd);
+hd44780_gotoxy(&lcd, 0, 0);
+hd44780_puts(&lcd, "Hello wo");
+hd44780_gotoxy(&lcd, 0, 1);
+hd44780_puts(&lcd, "rld!");
+```
+
+### 16x2, 20x2
+
+#### Memory layout
+
+![1602 display](img/1602.png)
+
+#### Example
+
+```C
+hd44780_t lcd = {
+    .addr = ADDR,
+    .font = HD44780_FONT_5X8,
+    .lines = 2,
+    .pins = {
+        .rs = 0,
+        .e  = 2,
+        .d4 = 4,
+        .d5 = 5,
+        .d6 = 6,
+        .d7 = 7,
+        .bl = 3
+    },
+    .backlight = true
+};
+```
+
+### 16x4, 20x4
+
+#### Memory layout
+
+![1604 display](img/1604.png)
+
+#### Example
+
+```C
+hd44780_t lcd = {
+    .addr = ADDR,
+    .font = HD44780_FONT_5X8,
+    .lines = 2,
+    .pins = {
+        .rs = 0,
+        .e  = 2,
+        .d4 = 4,
+        .d5 = 5,
+        .d6 = 6,
+        .d7 = 7,
+        .bl = 3
+    },
+    .backlight = true
+};
+```