vfd.c

#include <mega88a.h> // AVR Mega88 PA
#include <delay.h>   // Delay for-loop functions
#include <spi.h>     // SPI functions to talk with MAX6920SAWP -> VFD
#include <stdint.h>  // `uint8_t` and `uint16_t` 

#include "vfd.h"
#include "main.h"


volatile uint8_t stayAwake = SLEEP_TIMEOUT; // How long before going to sleep (20Hz counter counting to 0)

uint8_t vfdHour   = 255; // Init with display off
uint8_t vfdMinute = 255;



// Turn off VFD's high-voltage DC2DC boost converter (PD1)
void dc2dcOff(void) {
  PORTD &= ~(1 << PORTD1);
}


// Turn on VFD's high-voltage DC2DC boost converter (PD1) 
void dc2dcOn(void) {
  PORTD |= 1 << PORTD1;
}


// Turn off VFD's low-voltage filament heater (PB1) 
void fHeatOff(void) {
  PORTB &= ~(1 << PORTB1);
}


// Turn on VFD's low-voltage filament heater (PB1) 
void fHeatOn(void) {
  PORTB |= 1 << PORTB1;
}


// Turn off both DC2DC and filament heater
void vfdOff() {
  dc2dcOff();
  fHeatOff();
}


// Turn on both DC2DC and filament heater
void vfdOn() {
  dc2dcOn();
  fHeatOn();
  delay_us(500); // Give time for DC2DC to stabilise before displaying the time 
}


// Turn off all segments
// Almost duplication of the function below, but it's not implemented
// in a generic way because the CodeVisionAVR toolchain will not
// optimize things, even single instruction functions will not get
// inlined and this section needs to perform quickly
void clearVfd() {
  // Send 16-bit of zeros to the MAX6920AWP
  spi(0);
  spi(0);
               
  // Commit the 'clear screen' 
  // Set high the PD7 pin -> MAX6920AWP.LOAD signal.
  // Allowing the serially  shifted data to be read into the driver stage
  PORTD |= (1 << PORTD7);

  // MAX6920AWP needs 55ns for the VFD LOAD pulse being high, 1 instruction @ 8MHz takes 125ns  
  
  // Set low the PD7 pin -> MAX6920AWP.LOAD signal.
  // Returning back to original operation mode (shifting data)    
  PORTD &= ~(1 << PORTD7);
}


// Transfer data to VFD, at the time only 1 character will be displayed,
// to display full clock this call needs to be called 4-5 times
void sendDataToVfd(uint16_t data) {
  // Transfer 16-bits to the MAX6920AWP, only lower 12-bits will be kept, 
  // bit 12-15 will be truncated in the MAX6920AWP chip
  spi(data >> 8);
  spi(data & 0xff);
               
  // Start displaying the data on VFD 
  // Set high the PD7 pin -> MAX6920AWP.LOAD signal.
  // Allowing the serially  shifted data to be read into the driver stage
  PORTD |= (1 << PORTD7);
  
  // MAX6920AWP needs 55ns for the VFD LOAD pulse being high, 1 instruction @ 8MHz takes 125ns
  
  // Set low the PD7 pin -> MAX6920AWP.LOAD signal.
  // Returning back to original operation mode (shifting data)    
  PORTD &= ~(1 << PORTD7);
  
  delay_us(10);  // Displaying a character give it a moment to glow
                 
  // Clear the VFD after each character to remove ghosting between characters
  // and to make sure last character is disabled before going to super loop
  // forcing each segment to glow equal amount of time and have even brightness
  clearVfd();      
}



// Take `hour` and `minute` values and send the corresponding data
// to VFD which will display it
void displayTime() {

  //  --A--
  // |     |
  // F     B
  // |     |
  //  --G--
  // |     |
  // E     C
  // |     |
  //  --D--

  const uint16_t segments[] = {
    1 << VFD_A | 1 << VFD_B | 1 << VFD_C | 1 << VFD_D | 1 << VFD_E | 1 << VFD_F,               // 0 character
    1 << VFD_B | 1 << VFD_C,                                                                   // 1 character
    1 << VFD_A | 1 << VFD_B | 1 << VFD_G | 1 << VFD_E | 1 << VFD_D,                            // 2 character
    1 << VFD_A | 1 << VFD_B | 1 << VFD_G | 1 << VFD_C | 1 << VFD_D,                            // 3 character
    1 << VFD_F | 1 << VFD_G | 1 << VFD_B | 1 << VFD_C,                                         // 4 character
    1 << VFD_A | 1 << VFD_F | 1 << VFD_G | 1 << VFD_C | 1 << VFD_D,                            // 5 character
    1 << VFD_F | 1 << VFD_G | 1 << VFD_C | 1 << VFD_D | 1 << VFD_E,                            // 6 character
    1 << VFD_A | 1 << VFD_B | 1 << VFD_C,                                                      // 7 character
    1 << VFD_A | 1 << VFD_B | 1 << VFD_C | 1 << VFD_D | 1 << VFD_E | 1 << VFD_F | 1 << VFD_G,  // 8 character
    1 << VFD_A | 1 << VFD_F | 1 << VFD_B | 1 << VFD_G | 1 << VFD_C,                            // 9 character
  };                                     
  
  // Hours
  if (255 == vfdHour) {
    // Do not display hours
    sendDataToVfd(0);
    sendDataToVfd(0);
  } else {     
    // Regular display of hours
    uint8_t hourTens = vfdHour / 10;
    sendDataToVfd((0 == hourTens) ? 0 : segments[hourTens] | 1 << VFD_CH_1); // display blank if it's leading 0    
    sendDataToVfd(segments[vfdHour % 10]                   | 1 << VFD_CH_2);             
  }                                        
                    
  // The ':' dots
  sendDataToVfd(0                                          | (systick >= (SYSTICK_MAX/2))  << VFD_CH_3);
         
  // Minutes
  if (255 == vfdMinute) {
    // Do not display minutes
    sendDataToVfd(0);
    sendDataToVfd(0);
  } else {
    // Regular display of minutes
    sendDataToVfd(segments[(vfdMinute / 10) % 60]          | 1 << VFD_CH_4);    
    sendDataToVfd(segments[vfdMinute % 10]                 | 1 << VFD_CH_5);    
  }
}