OK. In that case it is a 32k Byte part.
--- Graham
==
On Friday, July 15, 2016 at 12:37:20 PM UTC-5, Bryan Wilcutt wrote:
>
> Graham,
> The part number is AT24c256 and a quick jot over to Atmel's trusty website
> and I found the spec sheet... "256K Serial Eeprom... organized as 512 pages
> of 64 bytes each."
>
> So, that should mean 512x64 = 32,768 bytes... .32K.
> 256k bits = 262,144 / 8 = 32,768 bytes... 32k.
>
> It's most certainly a 32k-byte part.
>
> Thanks,
> Bryan
>
> On Friday, July 15, 2016 at 11:45:02 AM UTC-5, Graham wrote:
>
>> Brian:
>>
>> You need to learn to speak "marketing" and "binary".
>>
>> A 32 k EEPROM (named by marketing) is a 32k BIT EEPROM.
>>
>> 32k BITs divided by 8 bits-per-byte is 4k BYTES.
>>
>> 4k BYTES is 0x1000 BYTES.
>>
>> So, your address space wraps around every 0x1000 BYTES.
>>
>> The data is not repeated every 0x1000 bytes, it is the SAME data.
>>
>> Sounds like your EEPROM is working just fine.
>>
>> --- Graham
>>
>> ==
>>
>> On Friday, July 15, 2016 at 10:47:54 AM UTC-5, Bryan Wilcutt wrote:
>>>
>>> I've been playing with the BBB 32k eeprom by reading and writing data to
>>> it. I use fseek(), fopen(), fread() and fwrite(). The device I am
>>> reading/writing/opening is:
>>> /sys/bus/i2c/devices/0-0050/at24-0/nvmem
>>>
>>> This does seem to work however not well. I noticed that the same data
>>> is repeated every 0x1000 bytes. Why is that? Am I not addressing the part
>>> correctly? Since I'm ultimately using the at24.c driver, I inspected it
>>> and it does seem to attempt to translate addresses for the part. Are there
>>> specific limitations with at24 that I should be aware of, nothing seems to
>>> be documented that I've seen.
>>>
>>> #define e2FILE "/sys/bus/i2c/devices/0-0050/at24-0/nvmem"
>>>
>>> int readEEPROMAt(unsigned char *p, unsigned int startAddr, unsigned
>>> int len)
>>> {
>>> int retVal = 0;
>>> FILE *fp = NULL;
>>>
>>> if ((fp = fopen(e2FILE, "r")) != NULL)
>>> {
>>> if (fseek(fp, startAddr, 0) == 0)
>>> {
>>> if (fread(p, 1, len, fp) != len)
>>> printf("Error: Cannot read EEPROM\n");
>>> else
>>> retVal = 1;
>>> } else {
>>> printf("Error: Could not index EEPROM, no data read.");
>>> }
>>> } else {
>>> printf("Error: Cannot open EEPROM\n");
>>> }
>>>
>>> if (fp)
>>> fclose(fp);
>>>
>>> return retVal;
>>> }
>>>
>>> Bryan
>>>
>>>
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