Use of Pullup resistors for an incoming bus.

Other Hardware General Electronics
1

I am capturing data that from industrial device that is meant to be printed by a dot matrix printer, the device uses RS232 -DB25 port. I am able to capture data successfully using Arduino UNO,using Pullup for Input Wires.
I am now trying to minimalize the circuit by making own pcb board using Arduino, do I need to add pullup register for all the data buses or a single pullup register can be used?

String oString;
String mainString;

#define Data0   5
#define Data1   6
#define Data2   7
#define Data3   8
#define Data4   9
#define Data5   10
#define Data6   11
#define Data7   12

#define nStrobe 2
#define nAck    3
#define Busy    4

enum States {
  READY,
  BUSY,
  ACK,
  STDBY
} State;

int inputLength = 0;

void setup()
{
  //--------- Configure pins --------------
  
  pinMode(nStrobe, INPUT_PULLUP);
  
  for (int n = Data0; n < (Data7+1); n++)
    pinMode(n, INPUT_PULLUP);
  
  pinMode(nAck, OUTPUT);
  pinMode(Busy, OUTPUT);
  
  Serial.begin(19200);
  while (!Serial) { ; }
  
  attachInterrupt(0,DataReady,FALLING);
  State = STDBY;
  delay(100);
}

Thank you.

2

I am capturing data that from industrial device that is meant to be printed by a dot matrix printer, the device uses RS232 -DB25 port. I am able to capture data successfully using Arduino UNO,using Pullup for Input Wires.
I am now trying to minimalize the circuit by making own pcb board using Arduino, do I need to add pullup register for all the data buses or a single pullup register can be used?

I think you mean pull up resistor.

You don't need pull up resistors for RS232 (or any other kind of resistors).

You do need to make sure the voltages are correct. 'Proper' RS232 uses (I think) + and - 12V. Arduino uses 5v or 3.3v depending on which one you have.

I can't comment about anything else you might be asking about.

3

Below is the full code, I'm using internal pullup resistors when using Arduino. But now I want to develop own PCB board. Do I need to attach seperate pullup resistors for each input?

String oString;
String mainString;

#define Data0   5
#define Data1   6
#define Data2   7
#define Data3   8
#define Data4   9
#define Data5   10
#define Data6   11
#define Data7   12

#define nStrobe 2
#define nAck    3
#define Busy    4


#include <SPI.h>
#include <SD.h>


enum States {
  READY,
  BUSY,
  ACK,
  STDBY
} State;

int inputLength = 0;

void setup()
{
  //--------- Configure pins --------------
  
  pinMode(nStrobe, INPUT_PULLUP);
  
  for (int n = Data0; n < (Data7+1); n++)
    pinMode(n, INPUT_PULLUP);
  
  pinMode(nAck, OUTPUT);
  pinMode(Busy, OUTPUT);
  
  Serial.begin(19200);
  while (!Serial) { ; }
  
  attachInterrupt(0,DataReady,FALLING);
  State = STDBY;
  delay(100);
}

               
void loop()
{

  while (Serial.available()>0) {
    char request = (char)Serial.read();
    if (request == 'k') {
      Serial.println("k");
      delay(20000);
      break;
    }
    

  }
  
  
  switch (State) {
    case READY:
      digitalWrite(Busy, LOW);
      digitalWrite(nAck,HIGH);
      break;
    case BUSY: // nStrobe signal received by interrupt handler
      digitalWrite(Busy, HIGH);
      ProcessChar();
      State = ACK;
      break;
    case ACK:
      digitalWrite(nAck,LOW);
      delayMicroseconds(10); // Specification minimum = 5 us       
      State = READY;
      break;
   
  }  

   
    if(inputLength>0){
      delay(10);
      if(Serial.read()==-1){
      processData();
    }
   }

}


void DataReady()
{
  State = BUSY;
}


void ProcessChar()
{
  
    byte Char;
  
  Char =  digitalRead(Data0) +
         (digitalRead(Data1) << 1) +
         (digitalRead(Data2) << 2) +
         (digitalRead(Data3) << 3) +
         (digitalRead(Data4) << 4) +
         (digitalRead(Data5) << 5) +
         (digitalRead(Data6) << 6) +
         (digitalRead(Data7) << 7);
         if (isDigit((char)Char) || (char)Char == 'g' || (char)Char == '.' || (char)Char == 'm') 
         {
            oString = oString+String((char)Char);
            inputLength++;
            }
}
  

void processData()
{
    Serial.println(oString);
    Serial.end();
    inputLength=0;
    oString="";
    delay(20);
    Serial.begin(19200);
}
4

Whether or not you need pull up resistors depends on what you are connecting to the inputs. To stand a chance of answering I, or anyone else on here, would need to see a circuit diagram. All I can say based on what you have said is you definitely don't need them for RS232 (but check the voltages).

5

RS232 is specified as +/-3 to +/-12V, so unless you check, a random RS232 device might well destroy
your Arduino unless some sort of voltage limiting or opto-coupler is used.