EEPROM page rotates while writing to it

Question

The following code intends to read from serial port and write the data byte by byte to a 24LC01B EEPROM.

// 24LC01B PINS
// Pin 1, A0: float
// Pin 2, A1: float
// Pin 3, A2: float
// Pin 4, VSS: GND
// Pin 5, SDA: Arduino A4
// Pin 6, SCL: Arduino A5
// Pin 7, WP: Write/Protect = GND
// Pin 8, VCC: +5


#include <Arduino.h>
#include <Wire.h>

// I2C Bus address of 24LC256 EEPROM;
// if more than one eeprom, they will have different addresses (h/w configured);
#define EEPROM_ADDR 0x50
byte m_addr = 0;

#define MAX_ADDRESS 128


byte eeprom_write(byte address, byte *data, byte len)
{  
    byte r = 0;
    for(byte i=0; i<len; )
    {
        Wire.beginTransmission(EEPROM_ADDR | m_addr);
        Wire.write(address + i); 
        byte l = len > 8 ? 8 : l;
        Wire.write(data+i, l);
        r |= Wire.endTransmission();
        delay(3);
        i += l;
    }
    return r;
}

byte eeprom_read(byte address, byte *data, byte len)
{
    Wire.beginTransmission(EEPROM_ADDR | m_addr);
    Wire.write(address);
    byte tr = Wire.endTransmission();
    if(tr)
        return tr;

    Wire.requestFrom((uint8_t)(EEPROM_ADDR | m_addr), len);
    byte avail = Wire.available();
    if(avail < len)
        return 0xFF;

    for(int i=0; i < len; i++)
    {
        // store data in raw bcd format
        data[i] = Wire.read();
    }
    return 0;
}

void setup()
{
    Wire.begin();
    Serial.begin(9600);
    delay(500);
    Serial.println("Type something to store in EEPROM");
}

byte i = 0;

void loop()
{
    if(Serial.available())
    {
        byte data = Serial.read();
        int rc = eeprom_write(i, &data, 1);
        if(rc==0)
        {
            Serial.print("EEPROM[0x");
            Serial.print(i, HEX);
            Serial.print("] = 0x");
            Serial.print(data, HEX);
            Serial.print(" (");
            Serial.print((char)data);
            Serial.print(")");
            Serial.println();

            Serial.println("Reading from EEPROM:");
            for(byte j=0;j<MAX_ADDRESS;j++)
            {
                if(byte rc=eeprom_read(j, &data, 1))
                {
                    Serial.print("Error in reading from EEPROM (rc=0x");
                    Serial.print(rc, HEX);
                    Serial.println(")");
                }
                else
                {
                    Serial.print(data, HEX);
                    Serial.print(' ');
                    if((j + 1) % 8 == 0 && j != MAX_ADDRESS - 1)
                        Serial.print("| ");
                }
            }
            Serial.println("");
        }
        else
        {
            Serial.println("Write error.");
        }
        i++;
    }
}

Every time I write one byte to the EEPROM, I read back the data on it. The result is a bit disappointing for me. I understand that 24LC01B has a page size of 8 bytes. But, it does not make sense to me why the bytes withing the page rotate right every time I write into it

Type something to store in EEPROM
EEPROM[0x0] = 0x61 (a)
Reading from EEPROM:
61 4 4F 0 80 0 80 4 | 4 45 0 80 4 3 0 70 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x1] = 0x62 (b)
Reading from EEPROM:
4 62 4 4F 0 80 0 80 | 4 45 0 80 4 3 0 70 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x2] = 0x63 (c)
Reading from EEPROM:
80 4 63 4 4F 0 80 0 | 4 45 0 80 4 3 0 70 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x3] = 0x64 (d)
Reading from EEPROM:
0 80 4 64 4 4F 0 80 | 4 45 0 80 4 3 0 70 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x4] = 0x65 (e)
Reading from EEPROM:
80 0 80 4 65 4 4F 0 | 4 45 0 80 4 3 0 70 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x5] = 0x66 (f)
Reading from EEPROM:
0 80 0 80 4 66 4 4F | 4 45 0 80 4 3 0 70 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x6] = 0x67 (g)
Reading from EEPROM:
4F 0 80 0 80 4 67 4 | 4 45 0 80 4 3 0 70 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x7] = 0x68 (h)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 4 45 0 80 4 3 0 70 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x8] = 0x69 (i)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 69 4 4F 0 80 0 80 4 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x9] = 0x6A (j)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 4 6A 4 4F 0 80 0 80 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0xA] = 0x6B (k)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 80 4 6B 4 4F 0 80 0 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0xB] = 0x6C (l)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 0 80 4 6C 4 4F 0 80 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0xC] = 0x6D (m)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 80 0 80 4 6D 4 4F 0 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0xD] = 0x6E (n)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 0 80 0 80 4 6E 4 4F | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0xE] = 0x6F (o)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 4F 0 80 0 80 4 6F 4 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0xF] = 0x70 (p)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 4 4F 0 80 0 80 4 70 | 3 F6 0 5B 4 38 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x10] = 0x71 (q)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 4 4F 0 80 0 80 4 70 | 71 4 4F 0 80 0 80 4 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF 
EEPROM[0x11] = 0x72 (r)
Reading from EEPROM:
4 4F 0 80 0 80 4 68 | 4 4F 0 80 0 80 4 70 | 4 72 4 4F 0 80 0 80 | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF | FF FF FF FF FF FF FF FF

Reading the code and serial EEPROM specifications takes a lot of time. Try this and if it works I'll provide a more complete answer: Write all 8 bytes in a page. — st2000, Dec 15 '19 at 16:26
@st2000, I actually have tried 8 bytes data writing and it worked fine. No problem with that. The problem raises when you write less than a page (8 bytes). Is writing minimum as much as size of the page anything standard requirements for EEPROMs? I have not seen something like that in the datasheets. — ar2015, Dec 16 '19 at 9:24
It doesn't matter if you write 1 byte or a complete page. the only import thing is, you do not cross a page border while writing. — theSealion, Dec 17 '19 at 10:49

Peter Paul Kiefer · Accepted Answer · 2019-12-16 16:41:17Z

The global variable data is a byte variable. But in the read and write function you use it as an byte array (data[i] or 'data +i'). That's not OK, but also not an error in the case you use length 1 ;-).

In your read function you performed a so called random read action that must be terminated by a STOP signal on the I2C bus. This can be forced by:

// ...

for(int i=0; i < len; i++)
{
    // store data in raw bcd format
    data[i] = Wire.read();
}

Wire.endTransmission(true);

return 0;

// ...

It's just a guess.

Writing single bytes must also be ended by a STOP condition but you used

r |= Wire.endTransmission();

that does not send a STOP signal.

Again you can force it with:

r |= Wire.endTransmission( true );

I'm not a Wire lib wizard, so I had read the Arduino documentation. Hopefully I understood it correctly.

theSealion · Accepted Answer · 2019-12-17 10:47:17Z

Your problem is

byte l = len > 8 ? 8 : l;

in the eeprom_write() function.

You wrote byte NumberOfBytes = len > 8 ? 8 : NumberOfBytes; and that will leads to an undefined behavior.

And for the future, if you want to write more than 1 Byte it is not important how many byte you write in a block but that the addresses are all located on the same eeprom page.

((address / pagesize) == ((address + length) / pagesize) must be true

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