Information

I
2
C Interface
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
17-20 Freescale Semiconductor
Figure 17-10. EEPROM Data Format for One Register Preload Command
— The first byte holds alternate configuration space (ACS), byte enables, and continue (CONT)
attributes.
— The 2 least-significant bits of the address are derived from
BYTE_ENABLES[ADDRESS_OFFSET]. Therefore, the address offset programmed into the
EEPROM preload should be a word offset.
— The most significant 16 bits (assuming 36-bit addressing) of the address are prepended from
either IMMRRBAR or alternate configuration space.
— After the first 3 bytes, 4 bytes of data should hold the desired value of the configuration register,
regardless of the size of transaction.
Byte enables should be asserted for any byte that will be written, and they should be asserted contiguously,
creating a 1, 2, or 4 byte write to a register. The boot sequencer assumes that a big-endian address is stored
in the EEPROM. In addition, byte enable bit 0 (bit 1 of the byte) corresponds to the most-significant byte
of data (data[0–7]), and byte enable bit 3 (bit 4 of the byte) corresponds to the least-significant byte of data
(data[24–31]).
By asserting ACS, an alternate configuration space address is prepended to the write request from the boot
sequencer according to the value in the ALTCBAR register. This will allow for external memories to be
configured. Otherwise, IMMRBAR is prepended to the EEPROM address.
If the CONT bit is cleared, the first 3 bytes, including ACS, the byte enables, and the address, should be
cleared 0. Also, the data contains the final CRC. A CRC-32 algorithm is used to check the integrity of the
data. The following polynomial is used:
1 + x
1
+ x
2
+ x
4
+ x
5
+ x
7
+ x
8
+ x
10
+ x
11
+ x
12
+ x
16
+ x
22
+ x
23
+ x
26
+ x
32
The CRC should cover all bytes stored in the EEPROM before the CRC. This includes the preamble, all
register preloads, and the first 3 bytes of the last 7-byte preload (which should be all zeros).
17.4.5.4 Boot Sequencer Done Indication
Dedicated hardware is not provided to indicate whether the boot sequencer operation completed
successfully. It is recommended that one of the GPIO signals be used for that purpose. To do this, the last
register preload programmed into the EEPROM should contain the address of the appropriate GPIO
01234567
ACS BYTE_EN CONT ADDR[12:13]
ADDR[14:21]
ADDR[12:29]
DATA[0:7]
DATA[8:15]
DATA[16:23]
DATA[24:31]