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IDT SMBus Interfaces
Notes
PES48H12G2 User Manual
Initialization from Serial EEPROM
During initialization from the optional serial EEPROM, the master SMBus interface reads configuration
blocks from the serial EEPROM and updates corresponding registers in PES48H12G2. Any software
visible register in the device may be initialized with values stored in the serial EEPROM.
All software visible registers have a system address. Configuration blocks stored in the serial EEPROM
use this system address shifted right two bits (i.e., configuration blocks in the serial EEPROM use DWord
addresses and not byte addresses).
– See Chapter 15, Register Organization, for the details on the system address and the address
map.
Since configuration blocks are used to store only the value of those registers that are initialized, a serial
EEPROM much smaller than the total size of all of the configuration spaces may be used to initialize the
device. Any serial EEPROM compatible with those listed in Table 13.1 may be used to store initialization
values.
Table 13.1 PES48H12G2 Compatible Serial EEPROMs
During serial EEPROM initialization, the master SMBus interface begins reading bytes starting at serial
EEPROM address zero. These bytes are interpreted as configuration blocks and sequential reading of the
serial EEPROM continues until the end of a configuration done block is reached or the serial EEPROM
address rolls over from 0xFFFF to 0x0. When a serial EERPROM address roll over is detected, loading of
the serial EEPROM is aborted, the Serial EEPROM Rollover (ROLLOVER) bit is set in the SMBus Status
(SMBUSSTS) register, and the RSTHALT bit is set in the SWCTL register.
A blank serial EEPROM contains 0xFF in all data bytes. When the PES48H12G2 is configured to
initialize from serial EEPROM and the first 256 bytes read from the EEPROM all contain the value 0xFF,
then loading of the serial EEPROM is aborted, the computed checksum is ignored, the Blank Serial
EEPROM (BLANK) bit is set in the SMBus Status (SMBUSSTS) register, and normal device operation
begins (i.e., the device operates in the same manner as though it were not configured to initialize from the
serial EEPROM).
This behavior allows a board manufacturing flow that utilizes uninitialized serial EEPROMs. See section
Programming the Serial EEPROM on page 13-5 for information on in-system initialization of the serial
EEPROM.
All register initialization performed by the serial EEPROM is performed in DWord quantities.
– Byte values may be modified by writing the entire DWord.
There are three configuration block types that may be stored in the serial EEPROM. The first type is a
single double word initialization sequence. A double word initialization sequence occupies seven bytes in
the serial EEPROM and is used to initialize a single double word register quantity.
A single double word initialization sequence consists of three fields and its format is shown in Figure
13.2. The TYPE field indicates the type of the configuration block. For single double word initialization
sequence, this value is always 0x0. The SYSADDR field contains the upper 16-bits of the global system
address of the double word to be initialized. The actual global system address, which is a byte address,
equals this value with two lower zero bits appended. The final DATA field contains the double word initializa-
tion value.
Serial EEPROM
24C32
24C64
24C128
24C256
24C512
13 - 2
Size
4 KB
8 KB
16 KB
32 KB
64 KB
April 5, 2013
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