Tri-state on 3.5

[elder0010]

Hello, I need to send a bits 0-7 of a byte using 8 pins of a 3.5 teensy, but since the pins are connected on a shared bus with an external device, i need to setup a tri-state logic, like this:

   - set the 8 pins to INPUT mode to disable output
   - wait for a certain event to happen
   - read a byte
   - "prepare" the byte data over 8 pins
   - send the byte data setting the pins to OUTPUT MODE
   - switch back to INPUT mode to disable output after a while
   - loop to start

In the example, D0/D7 pins are 23/16 (A9/A2) pins of a 3.5 teensy (so they are analog pins).

#define D0_PIN 23
#define D1_PIN 22
#define D2_PIN 21
#define D3_PIN 20
#define D4_PIN 19
#define D5_PIN 18
#define D6_PIN 17
#define D7_PIN 16

void setup(){
   [..] //init code not needed to show the problem
   disableOutput(); //set all D0,D7 pins to INPUT mode
}

void loop() {
  //wait for a certain condition to happen (address bus is stable)
  while ((address_current = readAddressBus()) != address_previous){
      address_previous = address_current;
  }
 
  if(cartEnabled == 1){
    returnByte = rom_buffer[address_current];
    //write the 8 bits to the pins set to INPUT mode
    digitalWrite(D0_PIN,returnByte&1);
    digitalWrite(D1_PIN,returnByte&2);
    digitalWrite(D2_PIN,returnByte&4);
    digitalWrite(D3_PIN,returnByte&8);
    digitalWrite(D4_PIN,returnByte&16);
    digitalWrite(D5_PIN,returnByte&32);
    digitalWrite(D6_PIN,returnByte&64);
    digitalWrite(D7_PIN,returnByte&128);
    enableOutput(); //set all D0,D7 pins to OUTPUT mode to send the byte data

    //wait until a new address is requested
    while(readAddressBus() == address_current);
    disableOutput(); //disable the output
  }
}

inline void enableOutput(){
  pinMode(D0_PIN,OUTPUT); 
  pinMode(D1_PIN,OUTPUT); 
  pinMode(D2_PIN,OUTPUT); 
  pinMode(D3_PIN,OUTPUT); 
  pinMode(D4_PIN,OUTPUT); 
  pinMode(D5_PIN,OUTPUT); 
  pinMode(D6_PIN,OUTPUT);
  pinMode(D7_PIN,OUTPUT); 
}

inline void disableOutput(){
  pinMode(D0_PIN,INPUT); 
  pinMode(D1_PIN,INPUT); 
  pinMode(D2_PIN,INPUT); 
  pinMode(D3_PIN,INPUT); 
  pinMode(D4_PIN,INPUT); 
  pinMode(D5_PIN,INPUT); 
  pinMode(D6_PIN,INPUT);
  pinMode(D7_PIN,INPUT); 
}

unsigned int readAddressBus(){
  a0 = digitalRead(A0_PIN);
  a1 = digitalRead(A1_PIN);
  a2 = digitalRead(A2_PIN);
  a3 = digitalRead(A3_PIN);
  a4 = digitalRead(A4_PIN);
  a5 = digitalRead(A5_PIN);
  a6 = digitalRead(A6_PIN);
  a7 = digitalRead(A7_PIN);
  a8 = digitalRead(A8_PIN);
  a9 = digitalRead(A9_PIN);
  a10 = digitalRead(A10_PIN);
  a11 = digitalRead(A11_PIN);
  cartEnabled = digitalRead(E_PIN);
  
  return (a0 | a1 <<1 | a2<<2 | a3<<3 | a4<<4 | a5<<5 | a6<<6 | a7<<7 | a8<<8 | a9<<9 | a10<<10 | a11<<11)&0xFFF;
}

...

Is this the correct approach? Thanks!