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NXP Semiconductors
PNX15xx/952x Series
Volume 1 of 1
Chapter 6: Boot Module
PNX15XX_PNX952X_SER_N_4
NXP B.V. 2007. All rights reserved.
Product data sheet
Rev. 4.0 — 03 December 2007
6-216
4.
The Boot From an I2C EEPROM
If none of the built-in scripts is suitable e.g., due to a different type of NAND-Flash or
a different memory organization or anything not matching the internal boot scripts, an
external serial boot EEPROM is required. Depending on the application
characteristics, this can be a small (1 Kilobyte or less) EEPROM that contains a small
boot script and starts the PNX15xx/952x Series system in host-assisted mode or
boot from Flash memory or ROM devices. Alternately, a large serial EEPROM can be
used to contain a complete disk le system or an upload capability from another
device than Flash/ROM.
For a 2-Kilobyte or smaller EEPROM, the script must start at byte address 1 (not 0).
For a 4-Kilobyte or larger EEPROM, the boot script must start at byte address 0. More
details in
Section 4.3. Each set of four successive bytes is assembled into a 32-bit
word value (the byte read rst ends up as the least signicant byte, LBS). The 32-bit
words are then interpreted as commands, as documented earlier in
Section 2.3.Remark: It has been seen that depending on the Write Protect pin status, some
EEPROMs do not behave the same way on a write of 0 bytes
(Section 4.3). The
internal counter gets or does not get incremented which makes this rule of where the
first byte is located at address 0 or 1 different. Refer to EEPROM datasheet or try both
options.
4.1 External I2C Boot EEPROM Types
The PNX15xx/952x Series Boot module supports all I2C EEPROMs (sometimes
called 2-wire EEPROMs) that use a 1-byte or 2-byte address protocol and respond to
an I2C device code 1010 (binary). Subtle differences exist between devices For
example:
It is recommended to avoid devices that have partial array write protection, since
such devices could be overwritten by accidental or intentional I2C writes, causing
boot failure during the next reset.
Some devices may have additional functionality that is useful, like a watchdog
timer or a power voltage drop sensor.
Availability from different vendors may vary.
Programming protocols may vary.
Table 10 lists a variety of devices. This list is by no means exhaustive, nor has
operation for all these devices been veried.
Table 10: Examples of I2C EEPROM Devices
Size
Device
Write Protection
Coverage
Address Protocol
Comment
256 bytes
ATMEL 24C02
Full Array
1 byte
512 bytes
ATMEL 24C04
Full Array
1 byte
1 kilobytes
ATMEL 24C08
Full Array
1 byte
Tested
2 kilobytes
NXP PCF85116-3
Full Array
1 byte