Electronic – how to display current time

avrmicrocontroller

I am using ATmega32-A micro controller, coding in C language and compiling using CodeVisionAVR compiler.

I want to display current time, I have tried with "time.h":

int main(void){
 time_t now; 
 time(&now); 
 printf("(percent)s", ctime(&now)); 
}

but it seems this compiler and hardware won't support time.h. I know that all AVRs don't have a RTC/calendar in them.

Is there any other way to display current time. I am very new to programming micro controllers. Can any one help me with some examples.

I don't want to add external hardware to the existing board now. I am displaying information on the PC (hyperterminal) using USART communication. Is there any possibility that I can get current time from PC? if there can you explain about it a little bit?

Best Answer

No ATmega32 AVR has an RTC/calendar built into it AFAICS.

Assuming that the reference is to an external battery backed RTC on the AVR board, there isn't any source for the current time on a board without an RTC chip. At best, the bootloader you use with the microcontroller may keep data on many milliseconds have elapsed since the board was powered on - within the tolerance of the clock source and allowing for any occasional missed timer interrupts.

If you do have an RTC chip configured on the board, with the correct time set up on it, there might be a suitable RTC library for that chip. Such a library would typically provide hour(), minute(), second() and other time retrieval methods for your code to use.

The generic time.h C header does not ship with, and therefore is not supported by, AVRdude or Arduino, apparently.

There is a good tutorial on using AdaFruit's RTC breakout board, here.

Related Solutions

Need help initializing display on ATmega162

I like the way you do serial port debugging, and the comments at each stage.

It appears that your display, like every other small character LCD display I've ever held in my hands, uses the Hitachi 44780 interface standard. May I ask why you aren't using some pre-tested off-the-shelf LCD library code?

Would something like the following work for you?

// WARNING: untested code. And therefore riddled with bugs.
#define SCREEN_ENABLE 4
#define SCREEN_READ 2
#define SCREEN_RS 1
// LCD #defines copied from http://techref.massmind.org/techref/io/lcd/44780.htm
#define LCDClearDisplay 1
#define LCDCursorHome   2
#define LCDOff      8   ;0x08 turn the display (and the cursor) off.
#define LCDOn       12  ;0x0C Turn on the display, but without a cursor
#define LCDCursorOn 14  ;0x0E Turn on the cursor (as an underline) as well as the display
#define LCDCursorBlink  15  ;0x0F Turn on a blinking block cursor as well as the display
#define LCDCursorLeft   16  ;0x10 Move the cursor left by one character
#define LCDCursorRight  20  ;0x14 Move the cursor right one letter
#define LCDShiftLeft    24  ;0x18 Shift the entire display left one character
#define LCDShiftRight   30  ;0x1C Shift the entire display right one character
#define LCDGoto     128 ;0x80 Add the location of the character position 
                ;   to which you wish to move the cursor

void screen_enable(void){
    _delay_us(2);
    PORTE |= SCREEN_ENABLE;
    _delay_us(2); // must be at least 140 ns
}
void screen_disable(void){
    PORTE &= ~SCREEN_ENABLE;
    _delay_us(2);
}
void Screen_Execute(void)
{
    screen_enable();
    screen_disable();
}

/** wait until screen is no longer busy */
void screen_busywait(void)
{
    char busy = 0x80;
    DDRA=0x00; // all inputs, to avoid fighting the screen outputs
    while(busy){
        // read busy flag
        PORTE |= SCREEN_READ; // read
        PORTE &= ~SCREEN_RS; // instruction: read busy flag and address
        screen_enable();
        // read busy bit while the Enable bit is high
        busy = PINA & 0x80;
        screen_disable;
        //BLINK_LED(500);
    }// wait until no longer busy

    // switch to "normal" "MCU writes to display" mode.
    PORTE &= ~SCREEN_READ; // write
    DDRA=0xFF;
}

void screen_send_instruction( char instruction ){
    PORTA=instruction;
    PORTE=0x00 + SCREEN_RS; // RS high: instruction
    DDRE=0xFF;
    DDRA=0xFF;
    Screen_Execute();
};

void Screen_init(void)
{    
    //BLINK_LED(1000);
    SEND_STRING("Starting initialization\r\n",0);
    // see http://techref.massmind.org/techref/io/lcd/44780.htm

    _delay_ms(15);
    SEND_STRING("Step 1 executing.\r\n",0);
    screen_send_instruction( 0x30 );
    _delay_ms(250);
    SEND_STRING("Step 1 complete.\r\n",0);

    screen_send_instruction( 0x30 );//second time
    _delay_ms(5);
    screen_send_instruction( 0x30 );//third time
    _delay_ms(1);

    SEND_STRING("Step 2 start.\r\n",0);
    screen_send_instruction( 0x38 ); // 8 bit interface, 2 line display, normal font
    SEND_STRING("Step 2 complete.\r\n",0);

    SEND_STRING("Step 3 start.\r\n",0);
    //BLINK_LED(1000);
    screen_busywait();
    screen_send_instruction( LCDOff );//screen off
    SEND_STRING("Step 3 complete.\r\n",0);

    screen_busywait();
    screen_send_instruction( 0x06 );// Entry mode: increment

    screen_busywait();
    screen_send_instruction( LCDClearDisplay );//cursor goes to home and screen is cleared

    screen_busywait();
    screen_send_instruction( LCDCursorOn );//screen on and underline cursor on.

    SEND_STRING("Step 4 start.\r\n",0);
    //BLINK_LED(1000);
    screen_busywait();
    screen_send_instruction( 0x14 );//Move the cursor right one letter (why????)
    SEND_STRING("Step 4 complete.\r\n",0);

    SEND_STRING("Step 5 start.\r\n",0);
    //BLINK_LED(1000);
    screen_busywait();
    screen_send_instruction( LCDCursorBlink );//Turn on a blinking block cursor as well as the display
    SEND_STRING("Step 5 complete.\r\n",0);
}

p.s.: Rather than use 11 pins of your MCU to control the display, some people sacrifice a little speed to gain back some of those pins: some control the LCD display with 7 pins of the MCU in 4-bit mode, others control their LCD display with 1 pin of the MCU.

Electronic – bit banging

Bit banging is creating the whole series of pulses in software, instead of relying on a piece of hardware inside the microcontroller.

Many microcontrollers have a hardware SPI, and then all you have to do is write a byte to the output register, and the SPI controller will shift the data out, and at the same time receive data from the slave. You can get an interrupt when the transfer is complete, and then read the received data.

But some microcontrollers don't have the SPI hardware on board and then you have to simulate it by doing everything manually. SPI has a number of different modes, I'll use this pulse diagram as an example:

enter image description here

So while a dedicated SPI controller takes care of all the pulses, data shifting and timing, when bit-banging you have to take every action yourself:

Make Slave Select low  
Short delay
Do 8 times
  Make the SCK (Serial Clock) pin low 
  Make the MOSI (Master-Out-Slave-In) pin high or low depending on bit 7 of the data  
  Add brief delay  
  Make the SCK output high
  Read MISO (Master-In-Slave-Out) pin
  Shift received data left, and shift the bit just read in as bit 0   
  Add brief delay  
  Shift the data byte 1 bit left
Make Slave Select high again

Bit-banging SPI is relatively simple, the code for bit-banging I2C for instance will be more complex, and you'll need a timer somehow if you want to bit-bang the UART protocol.

Best Answer

Related Solutions

Need help initializing display on ATmega162

Electronic – bit banging

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