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SRAM and Arduino

splatkillwill

I'm trying to interact with SRAM (MB8416A-15) with my Arduino.

This is my schematic:


And my code:image

#define WRITE 14
#define RAM_G 15
#define ENABLE 16


void write(uint8_t address, uint8_t data) {
  DDRD = B11111111;
  PORTB = address;
  digitalWrite(WRITE, LOW);
  digitalWrite(ENABLE, LOW);
  PORTD = data;
  delayMicroseconds(1);
  digitalWrite(ENABLE, HIGH);
  digitalWrite(WRITE, HIGH);
}


uint8_t read(uint8_t address) {
  uint8_t data;
  DDRD = B00000000;
  PORTB = address;
  digitalWrite(WRITE, HIGH);
  digitalWrite(ENABLE, LOW);
  delayMicroseconds(1);
  data = PORTD;
  digitalWrite(ENABLE, HIGH);
  digitalWrite(WRITE, HIGH);
  return data;
}


void setup() {


  // init


  Serial.begin(9600);


  // control
  pinMode(WRITE, OUTPUT);
  pinMode(RAM_G, OUTPUT);
  pinMode(ENABLE, OUTPUT);
  digitalWrite(WRITE, HIGH);
  digitalWrite(RAM_G, LOW);
  digitalWrite(ENABLE, HIGH);
  // address
  DDRB  = DDRB  | B00111111;
  PORTB = B00000000;
  // data
  DDRD = B00000000;


  // test


  write(B00000000, 10);
  Serial.println(read(B00000000));
  
  write(B00000001, 20);
  Serial.println(read(B00000000));
  Serial.println(read(B00000001));
  
  write(B00000010, 30);
  Serial.println(read(B00000000));
  Serial.println(read(B00000001));
  Serial.println(read(B00000010));
  
  write(B00000010, 40);
  Serial.println(read(B00000000));
  Serial.println(read(B00000001));
  Serial.println(read(B00000010));
  Serial.println(read(B00000011));


}

 

I'd expect an output of

10
10
20
10
20
30
10
20
30
40

 

but I get

10
20
20
30
30
30
40
40
40
40

  • From the output that you get it appears that your address isn't working so that you are always writing and reading the same address.  You should probably just do a static check to see if you are actually writing the correct address values.  Seems like you have lots of setup time and you can write and read data.

  • There are three issues I see with your circuit and code:

    1) The input data is in the PIND register, you're just reading back what you wrote to the PORTD output register (this is why your last output is repeating).

    2) When you set the pins to be inputs the data register (PORTD) will be controlling the internal pull-up resistors (I didn't find a good Arduino page on this, but the behavior is described in the Atmega328p datasheet), so you have to write all zeros to PORTD before reading PIND.

    3) You're using PORTD for the databus while also using the serial ports (for monitoring your program), which is using two of the pins for RX and TX. You can't have both at the same time. When the serial port is enabled those two pins are no longer connected to the PORTD register.

     

    I'd suggest that you write a nibble (4-bits) to the SRAM and see if that works first, you can safely use the upper half of PORTD. You can also write to the SRAM in slow motion as is suggesting. I'd probably go further and hook up LEDs to really see that the pins are actually doing what I'm expecting them too.

     

    For future improvements: If you're just reading the SRAM sequentially you can use a counter IC for the address lines.