ST10R272L - MEMORY ORGANIZATION
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Each bank can be directly addressed via the address bus, while ‘Programmable Chip Select
Signals’ can be used to select various memory banks.
Four different bus types are supported:
Memory model and bus mode are selected during reset by pin EA and PORT0 pins. For
further details about the external bus configuration and control refer to “EXTERNAL BUS
INTERFACE” on page 145.
External word- and byte-data can only be accessed via indirect or long 16-bit addressing
modes using one of the four DPP registers. There is no short addressing mode for external
operands. Any word-data access is made to an even byte address.
For PEC data transfers, the external memory in segment 0 can be accessed independently
of the contents of the DPP registers, via the PEC source and destination pointers.
The external memory is not provided for single bit storage and is not bit addressable.
3.3
Crossing memory boundaries
An address is implicitly divided into equally sized blocks of different granularity, and into
logical memory areas. Crossing the boundaries between these blocks (code or data) or
areas requires special attention.
Memory Areas are partitions of the address space that represent different kinds of memory.
These memory areas are: the internal RAM/SFR area and the external memory. Accessing
subsequent data locations that belong to different memory areas is no problem. However,
when executing code, the different memory areas must be switched explicitly via branch
instructions. Sequential boundary crossing is not supported and leads to erroneous results.
Note
Changing from the external memory area to the internal RAM/SFR area takes
place in segment 0.
8-bit segmented mode:
16 MByte with A23...A16 on Port 4 and A15...A0 on PORT0 or
PORT1.
Multiplexed 16-bit bus:
with address and data on PORT0 (Default after Reset).
Multiplexed 8-bit bus:
with address and data on PORT0/P0L.
Demultiplexed 16-bit bus: with address on PORT1 and data on PORT0.
Demultiplexed 8-bit bus:
with address on PORT1 and data on P0L.
Non-segmented mode:
64KByte with A15...A0 on PORT0 or PORT1.