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Figure 13-1. UCD3138 Boot ROM Execution After Power-On/Reset
The Boot Flash Checksum at address 0x07FC provides more sophisticated field upgradeability. It is useful
for cases which require an upgrade:
•
Via PMBus, but at a different PMBus address from the ROM's standard PMBus address
•
Via a serial port
•
With simple encryption for program security
All of these tasks can actually be accomplished with the Program Flash checksum as well – so long as the
upgrade is not interrupted. If the upgrade is interrupted before it is complete, the Program Flash checksum
will not be correct, and the Boot ROM will not pass control to the Program Flash.
With the Boot ROM, only the first 2K of the program flash must be correct. The customer program in the
Boot Flash area has the responsibility for verifying the integrity of the other 30K of the Program Flash,
which can contain the operating program for the power supply.
If the upgrade is interrupted, the Boot Flash area will still have a valid checksum, and the Boot Flash
program must be written to recover and request a new download.
SNIU028A – February 2016 – Revised April 2016
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Boot ROM Function
439
Boot ROM and Boot Flash
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