Discussion in "8051 Discussion Forum" started by    Abhinav    Jun 13, 2010.
Sun Jun 13 2010, 06:43 PM
Hi friends

i am a little confused while using AT24C04. like how many addresses are available for storing the data bytes?

The slave address is 1010 for all EEPROM'S so can we use 2 EEPROM's with one micro?

How to store values bigger that a byte in EEPROM?

i am using BASCOM for coding.

thank you all.
Sun Jun 13 2010, 07:57 PM
>The slave address is 1010 for all EEPROM'S so can we use 2 EEPROM's with one micro?
those are upper 4 bits of 7-bit address. the lower 3 bits are configurable which means yes you can use more than 1 rather total of 8 such EEPROMs at a time.

>How to store values bigger that a byte in EEPROM?
split them in 2 or 3 depending on how big your data is..
let say if its a 16-bit value then:
EEPROMWrite(Add, data>>8); // write first 8bits

sorry i am not good at bascom

before you calculate the size of sub address you need to know how much memory is addressable. lets take an example of 24C02 EEPROM.
24C02 is 2kbit = 2/8 kByte = 1/4Kb = 256bytes

so to accomodate 256 addresses you need 1 byte (00 to 255). so your sub address will only be of 1 byte.

now lets take case with 24C16
24C16 is 16Kbit = 16/8Kbyte = 2Kb = 2048 bytes
so we need atleast 2 bytes to accomodate 2048 addresses. so sub address now will be of 2 bytes in this case.

so you can see how we decide the internal data addresses of EEPROM.
Mon Jun 14 2010, 07:56 AM
Hi ajay

Thanks for a amazing detailed reply.

As per this website http://www.digchip.com/datasheets/parts/datasheet/054/AT24C04-10PC-1_8.php
we can connect maximum of-

AT24C01/02 = 8
AT24C04 = 4
AT24C08 = 2
AT24C16 = 1

because of their reducing hard wired addressing pins.

I cannot understand fully the meaning of below-

"AT24C04, 4K SERIAL EEPROM: Internally organized with 32 pages of 16 bytes each,
the 4K requires a 9-bit data word address for random word addressing"
as written in datasheet.

"The 4K is internally organized with 256 pages of 2-bytes each."
as described on digichip website.

thank you so much.

Mon Jun 14 2010, 02:25 PM
when addressing register there are two path, first on which page that register lies second what is the address of that register on that particular page.

you can assume MSB of address to be as page address and LSB as address of register on that page. so you can understand better what is page address and how it relates to register address.

even in 8051 we have page addressing of ram in which RAM is organized as 256 pages of 256 bytes each. so total accessible ram by 8051 is 256*256 = 65536 bytes. when interfacing external ram the page address is given by P2 and register address is given by P0. relate to it and you will understand.
Thu Jun 17 2010, 07:07 PM
hi ajay,

now i understood almost all things just one to ask that if start sending data bytes from address 0 then i think i have to send address(16) again after 16 bytes else first byte will be overwritten.

am i right ?

thanks
Thu Jun 17 2010, 07:20 PM
write operation will not work if you dont send a stop after page size limit of EEPROM.

You can see every EEPROM datasheet explains Page write operation differently from byte write operation. datasheet will provide you complete details.

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