parallel communication simulation problem

Question

Hi I am trying to send data(1 byte) from one arduino to another using parallel communication(a bus of 8 connections) and not using any library. However, the problem is the data gets corrupt all the time and what I am supposed to receive at receiver arduino is not what I send. The protocol that I made up is similar to uart protocol. There is ES pin and when it is low, transmission is started and when it is high, the transmission is ended. I think the problem could be related to wires that I use to connect two arduinos. There could be some noise induced that could flip bits in wires or the code is problematic. I am posting my code. Maybe you can help me get through this and help me to resolve my problem.

Sender code:

#define ES 8 //enable sampling
#define B0 0 //Bus 0
#define B1 1
#define B2 2
#define B3 3
#define B4 4
#define B5 5
#define B6 6
#define B7 7
const char dataToBeSent = 'C';
bool data_bit;

void setup() {
  pinMode(ES,OUTPUT);
  pinMode(B0,OUTPUT);
  pinMode(B1,OUTPUT);
  pinMode(B2,OUTPUT);
  pinMode(B3,OUTPUT);
  pinMode(B4,OUTPUT);
  pinMode(B5,OUTPUT);
  pinMode(B6,OUTPUT);
  pinMode(B7,OUTPUT);
  digitalWrite(ES,HIGH);
  delay(3000);
} 
void loop() {
  
 digitalWrite(ES,LOW); //transmission is started
 delay(10);

 for(int i = 0 ; i<8 ; i++){
    data_bit = dataToBeSent & (0x80 >> i);
    digitalWrite(i,data_bit);
 }
  delay(10);
  digitalWrite(ES,HIGH); //end transmission
  while(true){}
}

Receiver code:

#define ES 8 //enable sampling
#define B0 0 //Bus 0
#define B1 1
#define B2 2
#define B3 3
#define B4 4
#define B5 5
#define B6 6
#define B7 7

char rx_data;
byte rx_byte= 0;
bool rx_pin;

void setup() {
  Serial.begin(9600);
  pinMode(ES,INPUT);
  pinMode(B0,INPUT);
  pinMode(B1,INPUT);
  pinMode(B2,INPUT);
  pinMode(B3,INPUT);
  pinMode(B4,INPUT);
  pinMode(B5,INPUT);
  pinMode(B6,INPUT);
  pinMode(B7,INPUT);
  delay(1000);

}

void loop() {
  
  byte rx_byte= 0;
  
  while(digitalRead(ES) == HIGH){}
  delay(15);

  for(int i = 0 ; i<8 ; i++){
    rx_pin = digitalRead(i);
    Serial.print(rx_pin);
    if(rx_pin == 1){
      rx_byte |= (0x80 >> i);
    }
  }
 
 rx_data = rx_byte ;

 Serial.print("Received data: ");
 Serial.println(rx_data);

 delay(15);

 while(digitalRead(ES)== HIGH){}
 
}

Answer 1

You problem is that you are only using one phase of your "ES" clock, when in fact you should be using two.

In the first phase, where ES is high, is where you set the IO pins to represent your transmitted byte. Only once that is done can you then progress to the second phase, where ES is low, to indicate to the receiver that "I have set up my outputs, it's now time for you to read them".

So your transmitted code would flow like:

1. Set ES HIGH
2. Set output pins to represent the byte
3. Set ES LOW
4. Delay
5. Set ES HIGH

If you look at any timing diagrams for any protocol there will be places where the data is being written to the bus, and places where the data is considered stable and able to be read by the receiver. It's the job of the clock signal to indicate where these points in the protocol - to synchronise the receiver.

For example, here is the Centronics (parallel port) protocol:

The data changes while nStrobe is HIGH, and only when that data is "settled" is nStrobe brought LOW to tell the receiver it can read the data. Once nStrobe is taken HIGH again the data is changed to the next byte to transmit.