How to read & write to a 25aa1024 (1 Mbit SPI Bus Serial EEPROM) via 16F88

[Dave]

wolwil, Here it is again incase you didn't find it. Maxpages is set for 1023 x the number of 24LC1025's you have connected. The routine saves the last storage pointer in the last 2 locations of the last 24LC1025. Block is incremented once for each page. Before you start a clean write you would set block to 0 which is the first page. When you want to read back the data then you would call READ_WRITE_BLK1025 and block would have the last address written..

This routine is rock solid and I use it for accessing 4 x 24LC1025's for a total of over 4 gigabits of memoy to record Azmnuth,Elevation,East/West/Up/Down Sensor data and control flag information for about 2 months at 1 minute intervals... I hope this helps...

 
CNTRL_BYTE    CON    $A0        'CONTROL BYTE FOR 24LC1025 I2C EEPROM MEMORY (A0/A1 USED FOR CHIP SELECT)
MAX_PAGES    CON    4095    'MAXIMUM MEMORY STORAGE PAGES,(32 BYTES/MINUTE x 4 MINUTES x PAGES = TOTAL MINUTES)
 
'*********************************************************************
RW_EEPROM1025:        'READ FROM or WRITE TO SERIAL EEPROM
'*********************************************************************
    IF READ_WRITE = 1 THEN    'WRITE 128 BYTE BLOCK TO EEPROM
        IF BLOCK <> 0 THEN    'IF STARTING NEW PASS DON'T READ OLD LOCATION
            READ_WRITE = 0    'SET FOR BLOCK READ
            GOSUB READ_WRITE_BLK1025    'READ FROM SERIAL EEPROM NEXT AVAILABLE STORAGE BLOCK
            READ_WRITE = 1    'SET FOR BLOCK WRITE
        ENDIF
        DEVICE = BLOCK / 512    'SELECT WHICH PHYSICAL ADDRESS BOUNDRY & EEPROM
        ADDRESS = BLOCK << 7    'CALCULATE 12C ADDRESS TO STORE DATA TO
        CNTROL_BYTE = CNTRL_BYTE    'COPY CONTROL BYTE
        CNTROL_BYTE.1 = DEVICE.1    'SET LSB OF HARDWARE ADDRESS
        CNTROL_BYTE.2 = DEVICE.2    'SET MSB OF HARDWARE ADDRESS
        CNTROL_BYTE.3 = DEVICE.0    'SET 64K BLOCK BIT
        INTCON.7 = 0    'CLEAR GLOBAL INTERRUPT
        I2CWRITE SDA,SCL,CNTROL_BYTE,ADDRESS,[STR STOR_DATA\128]    'SAVE DATA TO 12C
        WRITEOCCURED = 1
        INTCON.7 = 1    'SET GLOBAL INTERRUPT
        PAUSE 6        'ALLOW TIME FOR I2C WRITE ~5Ms.
        BLOCK = BLOCK + 1    'INCREMENT FOR NEXT AVAILABLE BLOCK TO WRITE
        BLOCK = BLOCK MIN MAX_PAGES    'LIMIT TO n BLOCKS OF 128 BYTES
        GOSUB READ_WRITE_BLK1025    'WRITE TO or READ FROM SERIAL EEPROM LAST STORAGE BLOCK
    ELSE
        DEVICE = BLOCK / 512    'SELECT WHICH PHYSICAL ADDRESS BOUNDRY & EEPROM
        ADDRESS = BLOCK << 7    'CALCULATE 12C ADDRESS TO STORE DATA TO
        CNTROL_BYTE = CNTRL_BYTE    'COPY CONTROL BYTE
        CNTROL_BYTE.1 = DEVICE.1    'SET LSB OF HARDWARE ADDRESS
        CNTROL_BYTE.2 = DEVICE.2    'SET MSB OF HARDWARE ADDRESS
        CNTROL_BYTE.3 = DEVICE.0    'SET 64K BLOCK BIT
        INTCON.7 = 0    'CLEAR GLOBAL INTERRUPT
        I2CREAD SDA,SCL,CNTROL_BYTE,ADDRESS,[STR READ_DATA\128]    'LOAD IN ENTIRE BLOCK
        WRITEOCCURED = 1
        INTCON.7 = 1    'SET GLOBAL INTERRUPT
    ENDIF
    RETURN
 
'*********************************************************************
READ_WRITE_BLK1025:    'WRITE TO or READ FROM SERIAL EEPROM NEXT AVAILABLE STORAGE BLOCK
'*********************************************************************
    ADDRESS = 65534        'POINT TO LAST STORED DATA(WORD) ADDRESS
    DEVICE = MAX_PAGES / 512    'SELECT WHICH PHYSICAL ADDRESS BOUNDRY & EEPROM
    CNTROL_BYTE = CNTRL_BYTE    'COPY CONTROL BYTE
    CNTROL_BYTE.1 = DEVICE.1    'SET LSB OF HARDWARE ADDRESS
    CNTROL_BYTE.2 = DEVICE.2    'SET MSB OF HARDWARE ADDRESS
    CNTROL_BYTE.3 = DEVICE.0    'SET 64K BLOCK BIT
    IF READ_WRITE = 1 THEN
        INTCON.7 = 0    'CLEAR GLOBAL INTERRUPT
        I2CWRITE SDA,SCL,CNTROL_BYTE,ADDRESS,[BLOCK.LOWBYTE,BLOCK.HIGHBYTE]    'WRITE DATA POINTER TO 12C    
        WRITEOCCURED = 1
        INTCON.7 = 1    'SET GLOBAL INTERRUPT
        PAUSE 6        'ALLOW TIME FOR I2C WRITE ~5Ms.
    ELSE
        INTCON.7 = 0    'CLEAR GLOBAL INTERRUPT
        I2CREAD SDA,SCL,CNTROL_BYTE,ADDRESS,[BLOCK.LOWBYTE,BLOCK.HIGHBYTE]    'READ DATA POINTER FROM 12C    
        WRITEOCCURED = 1
        INTCON.7 = 1    'SET GLOBAL INTERRUPT
    ENDIF
    RETURN

Dave Purola,
N8NTA