Rainbow Electronics AT75C310 - Manual (Page 11)

AT75C310
11
Boot Mode
When the reset pin is deasserted, i.e., when the AT75C310
exits from reset state, the NDSRA/BOOTN pin is sampled.
If NDSRA/BOOTN is high, the ARM starts fetching from
address 0x00000000, which corresponds to the external
memory. In a typical application, the external memory
located at 0x00000000 is a nonvolatile memory containing
the application.
If NDSRA/BOOTN is low, the internal boot ROM is
remapped to 0x00000000 and the internal boot program is
executed.
The boot program configures the USART A, waits for a
sync pattern, undertakes handshake processes and copies
all the incoming serial data into the Oak A internal program
memory. Note that this memory is in the ARM memory
space whereas the Oak A memory is in reset. Following
download, the ARM executes a jump and starts to fetch out
of the Oak A program memory. The downloaded routine is
typically more complex and faster and is able to program a
true application into the Flash memory.
If the initial handshake process fails, the AT75C310 falls
back into the normal boot mode, i.e., out of the external
memory.
The assembly source code of the boot program is given in
section “Assembly Source Code – Boot Program” on page
126.