74HCT595N工作原理

這是一顆計數暫存晶片

可以使用序列的方式傳入Q0~Q7的狀態(high or low)到內部register，然後輸出時chip依照register值去拉Q0~Q7的狀態

可以使用少數腳位一次控制Q0~Q7的狀態，此外由於此chip可以串接，所以可以一次控制更多腳位


下列圖來源: http://arduino.cc/en/uploads/Tutorial/595datasheet.pdf

74HCT595N腳位:

• VCC:5V
• GND
• Ds: serial data in
• Q0~Q7: 8根輸出pin
• Q7': storage register對應到Q7的bit，最為多顆chip 串接用
• MR: (active low) 清空shift register
• OE: (active low) 
• 若OE拉low，STcp raising時，將storage輸出至Q0~Q7 
• 若OE拉high，Q0~Q7輸出為高阻抗(相當於沒接上這顆chip)
• SHcp: raising edge trigger, 觸發shift register shift 1 bit(新的1bit資料由Ds取)
• STcp: raising edge trigger

從文件可以知道，74HCT595N有兩個register(8bit):

1. shift register - 序列資料輸入時使用
2. storage register - 控制Q0~Q7輸出時為high or low

從文件可以知道，SHcp/STcp最高可運作在100Mhz(每個clock 10ns)

• 由此可得知下面範例SHcp/STcp拉high/low時，每次delay只要5ns，不過由於Arduino delay最小只能用1 micro second，所以設定delayMicroseconds(1)即可

基本原理

1. 透過序列的方式將資料傳入shift register
2. 將shift register資料傳入storage register
1. 每個SHcp raising edge，資料會一直輸入進去chip的shift register
1. Q0'~Q7'代表shift register的值
2. Serial date寫入方向:
1. Ds > Q0' > Q1' > Q2' > Q3' > Q4' > Q5' > Q6' > Q7'
3. 輸出到Q0~Q7

範例:

1. 連接
1. chip 接上VCC/GND
2. micro controller gpio 接上Ds/MR/OE/SHcp/STcp
2. 初始化:
1. Ds/MR/OE/SHcp/STcp全部拉low
1. 此時由於MR為low，shift register全部清為0
2. STcp LOW->HIGH->LOW，將shift register的值寫入storage register
1. 此時由於OE為LOW，storage register的值馬上會輸出至Q0~Q7
3. 資料寫至shift register
1. 將MR 拉HIGH
2. 將Q7的值設到Ds, SHcp LOW->HIGN->LOW將資料移入shift register
3. 將Q6的值設到Ds, SHcp LOW->HIGN->LOW將資料移入shift register
4. 將Q5的值設到Ds, SHcp LOW->HIGN->LOW將資料移入shift register
5. 將Q4的值設到Ds, SHcp LOW->HIGN->LOW將資料移入shift register
6. 將Q3的值設到Ds, SHcp LOW->HIGN->LOW將資料移入shift register
7. 將Q2的值設到Ds, SHcp LOW->HIGN->LOW將資料移入shift register
8. 將Q1的值設到Ds, SHcp LOW->HIGN->LOW將資料移入shift register
9. 將Q0的值設到Ds, SHcp LOW->HIGN->LOW將資料移入shift register
4. 將資料從shift register移到storage register
1. STcp LOW->HIGH->LOW
1. 此時由於OE為LOW，storage register的值馬上會輸出至Q0~Q7

實做:

• 使用MTADRL293D 電機驅動模組，其中
• Ds: Arduino pin 8
• MR: 固定拉high
• OE: Arduino pin 7
• SHcp: Arduino pin 4
• STcp: Arduino pin 12

Arduino可使用我寫的library操作74HCT595N:

• https://github.com/cy-arduino/arduino_lib_MTADRL293D <== 74HCT595N 控制的library包含在此

簡單控制74HCT595N的範例程式碼:

const int DS = 8;
const int OE = 7;
const int SHCP = 4;
const int STCP = 12;

void setup(){
  Serial.begin(115200);

  while (!Serial){
    ;
  }

  delay(1000);
  Serial.println("=== setup() ===");

  pinMode(DS, OUTPUT);
  pinMode(OE, OUTPUT);
  pinMode(SHCP, OUTPUT);
  pinMode(STCP, OUTPUT);

  digitalWrite(DS, LOW);
  digitalWrite(OE, HIGH); //Q0~Q7　維持高阻抗
  digitalWrite(SHCP, LOW);
  digitalWrite(STCP, LOW);
}

void loop(){
  Serial.println("=== loop() ===");
  delay(1000);

  //serial data input into serial register
  //Q0~Q7: 00001111
  Serial.println("##serial data input into serial register");
  digitalWrite(DS, HIGH);//Q7
  digitalWrite(SHCP, HIGH);
  delayMicroseconds(1);
  digitalWrite(SHCP, LOW);
  delayMicroseconds(1);
  digitalWrite(DS, HIGH);//Q6
  digitalWrite(SHCP, HIGH);
  delayMicroseconds(1);
  digitalWrite(SHCP, LOW);
  delayMicroseconds(1);
  digitalWrite(DS, HIGH);//Q5
  digitalWrite(SHCP, HIGH);
  delayMicroseconds(1);
  digitalWrite(SHCP, LOW);
  delayMicroseconds(1);
  digitalWrite(DS, HIGH);//Q4
  digitalWrite(SHCP, HIGH);
  delayMicroseconds(1);
  digitalWrite(SHCP, LOW);
  delayMicroseconds(1);
  digitalWrite(DS, LOW);//Q3
  digitalWrite(SHCP, HIGH);
  delayMicroseconds(1);
  digitalWrite(SHCP, LOW);
  delayMicroseconds(1);
  digitalWrite(DS, LOW);//Q2
  digitalWrite(SHCP, HIGH);
  delayMicroseconds(1);
  digitalWrite(SHCP, LOW);
  delayMicroseconds(1);
  digitalWrite(DS, LOW);//Q1
  digitalWrite(SHCP, HIGH);
  delayMicroseconds(1);
  digitalWrite(SHCP, LOW);
  delayMicroseconds(1);
  digitalWrite(DS, LOW);//Q0
  digitalWrite(SHCP, HIGH);
  delayMicroseconds(1);
  digitalWrite(SHCP, LOW);
  delayMicroseconds(1);

  delay(1000);

  //serial register -> storage register
  Serial.println("##serial register -> storage register");
  digitalWrite(STCP, HIGH);
  delay(10);
  digitalWrite(STCP, LOW);
  delay(10);

  delay(1000);

  //storage register -> Q0~Q7
  Serial.println("##storage register -> Q0~Q7");
  digitalWrite(OE, LOW);

  delay(1000);

  Serial.println("##finish");
  while(true){
    ;
  }
}

========================================================


相關連結

• http://ruten-proteus.blogspot.tw/2012/11/io-74hc595-ic.html
• http://arduino.cc/en/tutorial/ShiftOut#.Uw19LvmSyXo
• http://arduino.tw/articlesindex/extend-io/213-74hc595.html
• http://arduino.cc/en/uploads/Tutorial/595datasheet.pdf

待續