I'm trying to get my Uno communicating with an SRAM chip (Microchip 23LC512) via SPI.
As a simple verification, I write several bytes of data then go back and read them, and print it on the serial monitor. But, when I run my code I get this:
Memory status:
20 1010101
21 1010101
22 1010101
23 1010100
400 10101010
401 1010101
402 1010101
403 1010101
Memory addresses are 16 bit, shown in hex; values are in binary. In this case I wrote B10101010 to each memory address.
I can't find any consistent pattern--sometimes several bytes in a row are correct, others none. Here it looks like it's wrapping values from the back to the front?
Any help is very much appreciated!
The code:
// Read and write to SRAM via SPI
#include <SPI.h>
//Pin definitions:
#define CS 8
//SRAM SPI commands
#define READ 0x03 //READ and WRITE to be followed by 16 bit address
#define WRITE 0x02
#define RDMR 0x05 //read mode register
#define WRMR 0x01 //write mode register
#define RSTIO 0xFF //reset input mode
//Mode commands
#define BYTE 0x00
#define PAGE 0x80
#define SEQUENTIAL 0x40
void configureRAM(void); //declare function
//Incoming and outgoing start addresses (16 bit)
unsigned int cw_addr=0x0020;
unsigned int ccw_addr=0x0400;
byte incoming=0xFF; //incoming SPI data
byte cw_status[4];
byte ccw_status[4];
int i=0;
void setup()
{
Serial.begin(9600);
SPI.begin();
configureRAM();
//read CW memory status byte
digitalWrite(CS,LOW);
SPI.transfer(READ);
SPI.transfer(highByte(cw_addr));
SPI.transfer(lowByte(cw_addr));
for(i=0;i<4;i++)
{
cw_status[i]=SPI.transfer(0x00);
}
digitalWrite(CS,HIGH);
//read CCW memory status byte
digitalWrite(CS,LOW);
SPI.transfer(READ);
SPI.transfer(highByte(ccw_addr));
SPI.transfer(lowByte(ccw_addr));
for(i=0;i<4;i++)
{
ccw_status[i]=SPI.transfer(0x00);
}
digitalWrite(CS,HIGH);
//print results
Serial.println("Memory status:\t");
for(i=0;i<4;i++){
Serial.print(cw_addr+i,HEX);
Serial.write('\t');
Serial.println(cw_status[i],BIN);
}
for(i=0;i<4;i++){
Serial.print(ccw_addr+i,HEX);
Serial.write('\t');
Serial.println(ccw_status[i],BIN);
}
}
void loop()
{
}
//Configure RAM settings and clear memory status bytes.
//Initialize SPI before calling configureRAM()
void configureRAM(void)
{
SPI.setClockDivider(SPI_CLOCK_DIV2); //SPI clock at 8MHz
SPI.setDataMode(SPI_MODE0); //CPOL=0, CPHA=0
SPI.setBitOrder(MSBFIRST); //MSB first
pinMode(CS,OUTPUT);
digitalWrite(CS,LOW); //set to single SPI mode
SPI.transfer(WRMR);
SPI.transfer(RSTIO);
digitalWrite(CS,HIGH);
digitalWrite(CS,LOW);
SPI.transfer(WRMR); //Set data mode to sequential
SPI.transfer(SEQUENTIAL);
digitalWrite(CS,HIGH);
digitalWrite(CS,LOW);
SPI.transfer(WRITE); //clear outgoing memory status byte
SPI.transfer(highByte(cw_addr)); //16 bit address transferred one byte at a time
SPI.transfer(lowByte(cw_addr));
for(i=0;i<4;i++){
SPI.transfer(0xAA);
}
digitalWrite(CS,HIGH); //pulse CS
digitalWrite(CS,LOW);
SPI.transfer(WRITE); //clear incoming memory status byte
SPI.transfer(highByte(ccw_addr));
SPI.transfer(lowByte(ccw_addr));
for(i=0;i<4;i++){
SPI.transfer(0xAA);
}
digitalWrite(CS,HIGH);
}
