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hd44780-8b.c
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hd44780-8b.c
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/*
* ----------------------------------------------------------------------------
* "THE BEER-WARE LICENSE" (Revision 42):
* <joerg@FreeBSD.ORG> wrote this file. As long as you retain this notice you
* can do whatever you want with this stuff. If we meet some day, and you think
* this stuff is worth it, you can buy me a beer in return. Joerg Wunsch
* ----------------------------------------------------------------------------
*
* HD44780 LCD display driver
*
* The LCD controller is used in 4-bit mode with a full bi-directional
* interface (i.e. R/~W is connected) so the busy flag can be read.
*
* $Id: hd44780.c 2002 2009-06-25 20:21:16Z joerg_wunsch $
*/
#include "hd44780-8b-defines.h"
#include <stdbool.h>
#include <stdint.h>
#include <avr/io.h>
#include <util/delay.h>
#include "hd44780.h"
#define GLUE(a, b) a##b
/* single-bit macros, used for control bits */
#define SET_(what, p, m) GLUE(what, p) |= (1 << (m))
#define CLR_(what, p, m) GLUE(what, p) &= ~(1 << (m))
#define GET_(/* PIN, */ p, m) GLUE(PIN, p) & (1 << (m))
#define SET(what, x) SET_(what, x)
#define CLR(what, x) CLR_(what, x)
#define GET(/* PIN, */ x) GET_(x)
/* nibble macros, used for data path */
#define ASSIGN_(what, p, v) GLUE(what, p) = (v)
#define READ_(what, p) (GLUE(what, p))
#define ASSIGN(what, x, v) ASSIGN_(what, x, v)
#define READ(what, x) READ_(what, x)
#define HD44780_BUSYFLAG 0x80
/*
* Send one pulse to the E signal (enable). Mind the timing
* constraints. If readback is set to true, read the HD44780 data
* pins right before the falling edge of E, and return that value.
*/
static inline uint8_t
hd44780_pulse_e(bool readback) __attribute__((always_inline));
static inline uint8_t
hd44780_pulse_e(bool readback)
{
uint8_t x;
SET(PORT, HD44780_E);
/*
* Guarantee at least 500 ns of pulse width. For high CPU
* frequencies, a delay loop is used. For lower frequencies, NOPs
* are used, and at or below 1 MHz, the native pulse width will
* already be 1 us or more so no additional delays are needed.
*/
#if F_CPU > 4000000UL
_delay_us(0.5);
#else
/*
* When reading back, we need one additional NOP, as the value read
* back from the input pin is sampled close to the beginning of a
* CPU clock cycle, while the previous edge on the output pin is
* generated towards the end of a CPU clock cycle.
*/
if (readback)
__asm__ volatile("nop");
# if F_CPU > 1000000UL
__asm__ volatile("nop");
# if F_CPU > 2000000UL
__asm__ volatile("nop");
__asm__ volatile("nop");
# endif /* F_CPU > 2000000UL */
# endif /* F_CPU > 1000000UL */
#endif
if (readback)
x = READ(PIN, HD44780_D8);
else
x = 0;
CLR(PORT, HD44780_E);
return x;
}
/*
* Send one byte to the LCD controller. As we are in 4-bit mode, we
* have to send two nibbles.
*/
void
hd44780_outbyte(uint8_t b, uint8_t rs)
{
CLR(PORT, HD44780_RW);
if (rs)
SET(PORT, HD44780_RS);
else
CLR(PORT, HD44780_RS);
ASSIGN(PORT, HD44780_D8, b);
(void)hd44780_pulse_e(false);
}
/*
* Read one byte (i.e. two nibbles) from the LCD controller.
*/
uint8_t
hd44780_inbyte(uint8_t rs)
{
uint8_t x;
SET(PORT, HD44780_RW);
ASSIGN(DDR, HD44780_D8, 0x00);
if (rs)
SET(PORT, HD44780_RS);
else
CLR(PORT, HD44780_RS);
x = hd44780_pulse_e(true);
ASSIGN(DDR, HD44780_D8, 0xFF);
CLR(PORT, HD44780_RW);
return x;
}
/*
* Wait until the busy flag is cleared.
*/
void
hd44780_wait_ready(bool longwait)
{
#if USE_BUSY_BIT
while (hd44780_incmd() & HD44780_BUSYFLAG) ;
#else
if (longwait)
_delay_ms(1.52);
else
_delay_us(37);
#endif
}
/*
* Initialize the LCD controller.
*
* The initialization sequence has a mandatory timing so the
* controller can safely recognize the type of interface desired.
* This is the only area where timed waits are really needed as
* the busy flag cannot be probed initially.
*/
void
hd44780_init(void)
{
SET(DDR, HD44780_RS);
SET(DDR, HD44780_RW);
SET(DDR, HD44780_E);
ASSIGN(DDR, HD44780_D8, 0xFF);
_delay_ms(150); /* 40 ms needed for Vcc = 2.7 V */
hd44780_outbyte(HD44780_FNSET(1, 0, 0), 0);
_delay_ms(41);
hd44780_outbyte(HD44780_FNSET(1, 0, 0), 0);
_delay_ms(1);
hd44780_outbyte(HD44780_FNSET(1, 0, 0), 0);
_delay_us(370);
hd44780_outcmd(HD44780_FNSET(1, 1, 0));
hd44780_wait_ready(false);
hd44780_outcmd(HD44780_DISPCTL(0, 0, 0));
hd44780_wait_ready(false);
}
/*
* Prepare the LCD controller pins for powerdown.
*/
void
hd44780_powerdown(void)
{
ASSIGN(PORT, HD44780_D8, 0);
CLR(PORT, HD44780_RS);
CLR(PORT, HD44780_RW);
CLR(PORT, HD44780_E);
}