512K (256K+256K) ROM
By default, when
power is first applied or following a hardware reset,
the RAM is disabled and the ROM base address is set to
000000h. This is referred
to as Mode 0 or BV (Boot Vector) Mode.
The Stack Pointer (SP) will be loaded with the 32-bit
address stored in ROM address 000000h and the Program
Counter (PC) will be loaded with the 32-bit address
stored in ROM address 000004h.
In Mode 1 or RU
(RAM Unlocked) Mode the following applies:
The ROM base
address is fixed at FC0000h.
The RAM base
address is fixed at 000000h.
from Mode 0 to Mode 1 occurs automatically when an
address anywhere in the Mode 1 ROM address space
(FC0000h - FFFFFFh) is read, this action unlocks
(enables) the RAM and relocates the ROM.
BV Mode can be disabled if not required.