PIC microcontroller example 2: SAA1064 digital tube display based on I2C

Functions: The four digital tubes are divided into two groups, and the four buttons are also divided into two groups. Each group controls the addition and subtraction of the corresponding digital tube display data. The data is displayed cyclically between 0--99, and has a power-off protection function. The data before power-off is saved through 24LC01B. The program is simple and easy to read, which is a blessing for beginners (because I am also a novice)!

2. Device Introduction

1. Overview 
    SAA1064 is a 4-bit LED driver produced by Philips. It is a bipolar circuit with an I2C interface. This circuit is specially designed to drive a 4-bit seven-segment display with a decimal point. Two 2-bit displays can be switched through a multi-way switch. The device has an I2C bus slave transmitter and receiver inside, which can be programmed to 4 different slave device addresses through the input level of the address pin ADR. The internal mode controller can control each bit of the LED to enable it to work in static mode, dynamic mode, off mode and segment test mode. 
2. Pin function and package form 
    SAA1064 uses two package forms: 24-pin DIP and SOT. Figure 1 shows the pin arrangement of the 24-pin DIP package. The functions of the main pins are as follows:
    ADR (1): address input line;
    CEXT (2): internal oscillator capacitor input terminal, typical value is 2.7nF;
    P8~P1 (3~10): segment data output port 1;
    P9~P16 (15~22): segment data output port 2;
    MX1 (11): multiplexer output 1;
    MX2 (14): multiplexer output 2:
    VEE (12): ground;
    VCC (13): power supply;
    SDA (23): I2C bus serial data line;
    SCL (24): I2C bus serial clock line; 
3. Functional Description 
3.1 Communication Protocol 
    The master device CPU reads or writes SAA1064 through the I2C bus. The information transmission format on the I2C bus in the read/write mode is shown in Figure 2. In the figure: S is the start signal; P is the end signal; A is the response bit; X is an arbitrary value; A1A0 is determined by the ADR input potential to determine the 2-bit address bit; SC SB SA is the unit address bit; C6~C0 is the control bit; PR is the power-on reset flag.
3.2 SAA1064 Slave Address
    The slave address of SAA1064 is determined by the input level on the pin ADR. The ADR pin corresponds to 4 different slave addresses (A1A0=00, 01, 10, 11) when connected to VEE, 3/8VCC, 5/8VCC and VCC respectively. In the write mode, the corresponding slave address byte values ​​are 70H, 72H, 74H, 76H, and in the read mode, the corresponding slave address byte values ​​are 71H, 73H, 75H, 77H. Other addresses are not responded to by the device.
3.3 Status Byte
    Only one bit is used in the status byte of SAA1064: the power-on reset flag bit PR. When it is logic "1", it indicates that power has been turned off and on since the last read status. After the read status byte operation is completed, the flag is cleared to 0.
3.4 Unit address
    bits SC, SB, and SA form a pointer to determine which register the data byte after the instruction byte is written to, and the other data is written to the subsequent unit in sequence. This feature is called unit address increment. The unit address pointer range is 0 to 7. The unit address allocation is listed in Table 1. 
3.5 Control Byte
    The meaning of each bit of the control byte (C0~C6) is as follows:
    C0=0 static display, digits 1 and 2 can be displayed continuously;
    C0=1 dynamic display, digits 1, 3 and 2, 4 are displayed alternately;
    C1=0/1 digits 1, 3 dark/light selection bit;
    C2=0/1 digits 2, 4 dark/light selection bit;
    C3=1 all segments are turned on for segment testing, and their current is determined by C4, C5, C6;
    C4=1 segment output current increases by 3mA;
    C5=1 segment output current increases by 6mA;
    C6=1 segment output current increases by 12mA;
3.6 Data Byte
    When the data in the data byte is 1, the corresponding segment is turned on (lit). Data bytes D17~D10, D27~D20, D37~D30, D47~D40 correspond to the displays of bits 1, 2, 3 and 4 respectively. The high bit corresponds to the output terminal P8 or P16, and the low bit corresponds to the output terminal P1 or P9. The data displayed by displays 1~4 corresponds to the content of unit addresses 1~4.
3.7 SDA, SCL
    SDA and SCL are the data line and clock line of the bus respectively. To prevent overvoltage pulses on these pins, a voltage regulator (5.5V) should be connected to them, that is, the normal line voltage should not exceed 5.5V. Under normal circumstances, the data jumps and latches on the clock of the corresponding bit.
3.8 Power-on reset
    The power-on reset signal is generated inside the SAA1064 chip. This signal can clear each bit inside to 0 and display all dark. At this time, only the power-off flag is set.
3.9 External timing control capacitor
    Connecting a timing capacitor to the ground on the pin (pin 2) of SAA1064 can make the internal multiplexed oscillator work. In static working mode, because the oscillator is not required to work, this pin can be connected or floating.
3.10 Segment data output terminals
    P1~P16 are segment data output terminals with controllable absorption current. Their conduction can be controlled by the corresponding digital bits, and the magnitude of their current is controlled by the control bits of C4, C5, and C6.
3.11 Multiple output terminals
    The multiple output terminals MX1 and MX2 of SAA1064 are alternately turned on in dynamic display mode. They are all driven by the frequency-divided signal of the internal clock.
    In static mode, MX1 is always turned on, and its output is composed of an internal emitter follower, which can directly drive the common pole of the 2-digit display. If it exceeds the total power consumption of the circuit, pins 11 and 14 should be connected together with a transistor.
III. Program (PICC adjustment)

//Use for DN-100 Cotroller
//Date:from 2007.12.7 to
//Author:wujie
//Company:Wuxi Zhouxiang complete set of welding equipment CO.LTD

//Introduce:
//MCU:p16f73
//display IC:SAA1064 addr:0x70    

//START
#include

__CONFIG(XT&WDTDIS&BORDIS);

//Program declaration

void initial(void);
void display(char cur_hex,char time_hex);
void button_test(void);
void start_iic();
void stop_iic(void);
void ack_iic();
void nack_iic();
void send_iic(char c);
char receive_iic(void);
 
//Predefined
#define nop() asm("nop")
#define SDA RC4
#define SCL RC3

unsigned int i,rxbuf;
char cur,time;
 
//Initialization
void initial(void)
{
 TRISA=0X3F; //ALL PORTS ARE INPUT
 PORTA=0X00;
 TRISB=0X03; //RB0,RB1 ARE INPUTS
 PORTB=0X00;
 TRISC =0XE7; // RC3,RC4, ARE outPUTS
 PORTC=0X18; //RC3,RC4 ARE IN HIGH
 
 cur=0;
 time=0;
  }
 
//Display subroutine
void display(char cur_hex,char time_hex)
{
 char d1buf, d2buf,d3buf,d4buf;

//Array storage display 7-segment code
 char bit_dis[]={0xfc,0x60,0xda,0xf2,0x66,0xb6,0xbe,0xe0,0xfe,0xf6,0xee,0x3e,0x9c,0x7a,0x9e,0x8e,0x00};
 
 d2buf=bit_dis[cur_hex%10];//unit digit of CUR
 d1buf=bit_dis[cur_hex%100/10];//tens digit of CUR
 d4buf=bit_dis[time_hex%10];//unit digit of TIME
 d3buf=bit_dis[time_hex%100/10];//tens digit of TIME
 nop();
 start_iic();
 nop();
 send_iic(0x70);//SAA1064 address
 send_iic(0x00);
 send_iic(0x37);//check the above information
 send_iic(d1buf);
 send_iic(d2buf);
 send_iic(d3buf);
 send_iic(d4buf);
 nop();
 stop_iic();
} 

 //write 24cl01b subroutine
void w_24cl01b(unsigned char cur_tmp,unsigned char time_tmp)
{
 start_iic();
 send_iic(0xa0);
 send_iic(0x10);
 send_iic(cur_tmp);
 send_iic(time_tmp);
 stop_iic();
 for(i=0 ;i<500;i++);
}
 
//read 24cl01b subroutine
char r_24cl01b()
{
 start_iic();
 send_iic(0xa0);
 send_iic(0x10);
 start_iic();
 send_iic(0xa1);
 cur=receive_iic();
 ack_iic( );
 time=receive_iic();
     nack_iic();
 stop_iic();
 display(cur,time);
 for(i=0;i<10000;i++);
 }
//Button detection
void button_test(void)
{
 if(RC1==1)
 {
  for(i=0;i<=2000;i++);//Delay 20mS
  if(RC1==1)
  {
   cur++;
   cur=cur %100; //Let CUR < 100, because only 2 digits can be displayed

   w_24cl01b(cur,time);
  }
 }
 if(RC2==1)
 {
  for(i=0;i<=2000;i++);
  if(RC2==1)
  {
   cur--;
   if(cur<=0)

   w_24cl01b(cur,time);//Write to 24LC01B and save
   {
    cur=cur+100;//Let CUR>0, because only 2 digits can be displayed
   }
      }
 }
 if(RC5==1)
 {
  for(i=0;i<=2000;i++);
  if(RC5==1)
  {
   time++;
   time=time%100;//Let TIME<100, because only 2 digits can be displayed

   w_24cl01b(cur,time);
  }
 }
 if(RC6==1)
 {
  for(i=0;i<=2000;i++);
  if(RC6==1)
  {
   time--;

   if(time<=0)
   {
    time=time+100; //Let TIME>0, because only 2 digits can be displayed
   }

    w_24cl01b(cur,time);
  }
 }
 display(cur,time);
 for(i=0;i<10000;i++);
}
 
//I2C protocol

//Start signal

void start_iic()
{
 SDA=1;
 SCL=1; nop  (
 ); nop()  ;  nop(); nop();  SDA=0;  nop();  nop();  SCL=0;//it is ready to send data  nop(); } //Stop signal void stop_iic(void) {  SDA=0;  SCL=1;  nop();  nop();  nop();  nop();  SDA=1;  nop(); }









 

//Send response

void ack_iic()
{
 SDA=0;
 nop();
 nop();
 SCL=1;
 nop();
 nop();
 nop();
 nop();
 SCL=0;
 nop();
 nop();
}

//Send a byte

void send_iic(char c)
{
 for(i=0;i<8;i++)
 {
  SCL=0;
  if((c<   {
   SDA=1;
  }
  else
  {
   SDA=0;
  }
  SCL=1;
  nop();
  nop();
  nop();
  nop();
  SCL=0;
  nop();
 }
  SDA=1;
  TRISC4=1;//Set to input state, wait for response
  SCL=1;//Assume that the response has always been
  nop();
  nop();
  nop();
  nop();
  SCL=0;
  nop();
  TRISC4=0;//Restore to output
}

//Accept a byte

char receive_iic(void)
{
 SDA=1;
 rxbuf=0;
 TRISC4=1;//Note: must set input
 for(i=0;i<8;i++)
 {
  SCL=0;
  nop();
  nop();
  nop();
  nop();
  SCL=1;
  nop();
  rxbuf=rxbuf<<1;
  if(SDA==1)
  {
   rxbuf=rxbuf+1;
  }
 }
 nop();
 nop();
 SCL=0;
 nop();
 TRISC4=0;//Restore to output
 return (rxbuf);
}

//Main program

void main(void)
{ 
 initial();

r_24cl01b(); //Read the data stored in 24LC01B before power failure

 while(1)
 {
  button_test();
  }
}

IV. Conclusion

           Pay attention to the purple areas in the above program. I have suffered losses from this before. The so-called tuned programs on the Internet do not pay attention to these areas, which results in the program not running normally as expected.