Effect: This command will tell you if it’s possible to read from or write to the mega168’s EEPROM. Sending a second byte (either the NULL command or a junk data byte) over the SPI once the return value is loaded will transfer it to the mega644’s SPDR. It is recommended you do not begin transmission of this second byte until 3 us after the transmission of the command byte has completed. This is to make sure the mega168 has time to load the SPDR. If SPDR is zero, EEPROM is readable and writable. Otherwise, reading and writing are not presently allowed. You may wish to send this command before attempting to read from or write to the mega168’s EEPROM, though both the read and write commands also return success/failure indicators.
Note: if you are running firmware version 1.00, you should ensure EEPROM remains readable/writable for some short duration (e.g. 300 us) before attempting a read or write.
Values sent: none
command byte = 254