Example: How to Use Page Write Feature of I2C EEPROMs

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' Omer YILDIZ , Istanbul/TURKEY ' May-2008 ' Sayzer @ www.picbasic.co.uk/forum ' This code is to show how to use the page write feature of I2C eeproms. ' Page write feature allows us to write an entire page at one shot, ' and takes one write cycle to complete. ' This code will accept 128-byte packet from RS232 port @9600bps, ' and write the entire packet into 24C512 external eeprom at one shot. ' Incoming 128-bytes packets must have at least 15mS intervals. ' Page size is different from eeprom to eeprom. ' For example: Page size for 24C512 is 128 bytes while ' it is 32 bytes for 24LC64. ' That means, we can write 128-bytes into the eeprom ' at once and it takes only approx 5 - 10 ms. ' If we had to do this one byte at a time, we would have to wait ' approx. 1 second to complete. ' 1 second may not sound that long but, ' think about 64,000 byte waiting to be written !! ' PIC18F452 ' Set your fuse settings up here. DEFINE OSC 20 'Thanks to DT INCLUDE "DT_INTS-18.bas" ' Base Interrupt System INCLUDE "ReEnterPBP-18.bas" ' Include if using PBP interrupts 'Thanks to Steve. DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1 DEFINE HSER_SPBRG 129 ' 9600 Baud @ 0,16% DEFINE HSER_CLROERR 1 ' Clear overflow automatically 'Thanks to MicroChip. ADCON1 = 7 TrisA = %000000 TrisB = %00000000 TrisC = %10000000 'RC7 => RS232 RX (input pin). TrisD = %00000000 TrisE = %000 PortA = 0 PortB = 0 PortC = 0 PortD = 0 PortE = 0 I2C_SCL VAR PortC.3 I2C_SDA VAR PortC.4 AdrW VAR WORD ' Address variable for write operation. AdrR VAR WORD ' Address variable for read operation. Mem VAR BYTE[1350] ' Create an array as large as possible. RXFlag VAR BIT ' Just a flag. Writetime CON 15 ' This is the write cycle time for external eeprom. (mS) PageSize CON 128 ' Page size for 24C512 : 128 bytes; for 24LC64 : 32 bytes. '====This is DT's famous and useful Int routine. ========= ASM INT_LIST macro ; IntSource, Label, Type, ResetFlag? INT_Handler RX_INT, _ReadPort, PBP, yes endm INT_CREATE ; Creates the interrupt processor ENDASM @ INT_ENABLE RX_INT ; Enable RX232 RX interrupt Begin: ' Initial adr values are zero. RXFlag = 0 AdrW = 0 AdrR = 0 Start: I2CREAD I2C_SDA, I2C_SCL,$A1,AdrR, [STR Mem\PageSize] ' Read one page from EEPROM and store into mem array. AdrR = AdrR + PageSize 'First page: 0-127 'Second page: 0 +128 = 128 (128 - 255) 'Third page: 128 +128 = 256 (256 - 383) '....etc.. ' Do your stuff .... GOTO Start ReadPort: HSERIN [STR Mem\PageSize] ' Store 128-byte (0-127) incoming packet into Mem array. I2CWRITE I2C_SDA, I2C_SCL,$A0,AdrW,[STR Mem\PageSize] ' Starting from addresss location = Adr, ' ...write 128-byte mem elements into EEPROM at one shot. '...Adr is the start address of the page in line. PAUSE Writetime ' For 24C512, 15ms is more then good enough. ' For LC series, 5-6 ms should be ok. AdrW = AdrW + PageSize ' For the next page write, increment EEPROM address ' ...with the size of one page. RXFlag = 1 ' Set a flag for use in main loop. @ INT_RETURN

Thanks Sayzer,
I will try this out.
JS

Hi Sayzer.

As the PBP manual states, the control byte must have bit 0 cleared. Is there any special reason that you have made it 1 in this command?

I2CREAD I2C_SDA, I2C_SCL,$A1,AdrR, [STR Mem\PageSize]

But here you still have it cleared:

I2CWRITE I2C_SDA, I2C_SCL,$A0,AdrW,[STR Mem\PageSize]

Regards,
Ioannis

Quote:

Originally Posted by Ioannis

Hi Sayzer.

As the PBP manual states, the control byte must have bit 0 cleared. Is there any special reason that you have made it 1 in this command?

I2CREAD I2C_SDA, I2C_SCL,$A1,AdrR, [STR Mem\PageSize]

But here you still have it cleared:

I2CWRITE I2C_SDA, I2C_SCL,$A0,AdrW,[STR Mem\PageSize]

Regards,
Ioannis

Hi Ioannis,

The way I read the data sheet of 24C512 eeprom, the write bit is 0 and the read bit is 1.
Same as 24LC64, 24LC512 also.

I agree that it is confusing, but it is a fact that for read operation either 0 or 1 works anyway.

Yes, the data sheet clearly states that bit 0 defines read or write. But PBP manual on I2C commands, says that this bit must be kept at 0. May be the compiler takes care of it. Anyway, I am sure it works just fine.

Ioannis

PBP handle the R/W bit for you.