Using Serial EEPROM  AT24LC128 for booting in AN2131

Question: An AT24LC128 serial EEPROM is used for booting, but the boot process from the EEPROM is not reliable. Why?

 

Answer:

The problem is that AN2131 requires stretch values be set for some I2C parts. The AT24LC128 part which runs at 3.3 Volts is a 400 KHz maximum part, but the timing between the two part may require the stretch value be set. The default boot uses a 90.9 KHz clock on the I2C bus so both 100K Hz and 400 KHz parts will work. This bus frequency can not be increase in the AN21xx series of parts. See Errata on Rev E silicon errata revision 1.2.