System.Hardware.PiLcd.Hd44780

This module lets you control an HD44780U Dot Matrix Liquid Crystal Display Controller/Driver (datasheet), such as the one used in the Adafruit LCD+Keypad Kit.

Only supports 4-bit mode, write only. The user specifies a callback for performing the actual I/O to the chip.

Access to the LCD is not threadsafe (you'll need to do your own locking), but it is safe in the presence of async exceptions.

Documentation

data LcdBus

Argument to lcSend. Specifies the state of the bus going to the HD44780. The RW line is always 0, because we only do writes.

Constructors

LcdBus

Fields

• lbRS :: !Bool

  Register Select

• lbE :: !Bool

  Enable

• lbDB :: !Word8

  4 LSB are DB4 to DB7

Instances

Eq LcdBus

Methods

(==) :: LcdBus -> LcdBus -> Bool

(/=) :: LcdBus -> LcdBus -> Bool

Ord LcdBus

Methods

compare :: LcdBus -> LcdBus -> Ordering

(<) :: LcdBus -> LcdBus -> Bool

(<=) :: LcdBus -> LcdBus -> Bool

(>) :: LcdBus -> LcdBus -> Bool

(>=) :: LcdBus -> LcdBus -> Bool

max :: LcdBus -> LcdBus -> LcdBus

min :: LcdBus -> LcdBus -> LcdBus

Read LcdBus

Methods

readsPrec :: Int -> ReadS LcdBus

readList :: ReadS [LcdBus]

readPrec :: ReadPrec LcdBus

readListPrec :: ReadPrec [LcdBus]

Show LcdBus

Methods

showsPrec :: Int -> LcdBus -> ShowS

show :: LcdBus -> String

showList :: [LcdBus] -> ShowS

newtype LcdCallbacks

Callback for communicating with the HD44780.

Constructors

LcdCallbacks

Fields

• lcSend :: LcdBus -> IO ()

  Sets the values on the bus. If using a direct parallel interface on a fast processor, you may need to insert a brief (500 ns) delay after writing to the bus. (This is unnecessary on the LCD+Keypad Kit, because the I²C operation of the MCP23017 provides more than enough delay.)

lcdInitialize :: LcdCallbacks -> IO ()

Initializes the LCD and clears the screen. You must call this function first, before any of the other LCD functions.

lcdClear :: LcdCallbacks -> IO ()

Clears the screen.

lcdControl

Arguments

:: LcdCallbacks

-> Bool

Enable display

-> Bool

Enable underline cursor

-> Bool

Enable blinking block cursor

-> IO ()

Controls what is shown on the LCD.

lcdWrite

Arguments

:: LcdCallbacks

-> Word8

Line number. Must be 0 or 1. (Even displays with four physical lines are modeled internally as 2 lines.)

-> Word8

Column number, starting at 0.

-> ByteString

Characters to write to the display. Must be encoded in the controller's native character encoding. See Table 4 on pages 17-18 of the HD44780U datasheet.

-> IO ()

Writes text onto the screen. To position the cursor without writing anything, you can write a zero-length string.

lcdDefineChar

Arguments

:: LcdCallbacks

-> Word8

The character code to define. Must be 0-7.

-> [Word8]

The bitmap data. Must be 8 bytes, with data in the least significant 5 bits of each byte.

-> IO ()

Defines a custom character.