ST6208C/ST6209C/ST6210C/ST6220C
MEMORY MAP (Cont’d)
3.1.2 Program Space
such as constants and look-up tables in OTP/
EPROM.
Program Space comprises the instructions to be
executed, the data required for immediate ad-
dressing mode instructions, the reserved factory
test area and the user vectors. Program Space is
addressed via the 12-bit Program Counter register
(PC register). Thus, the MCU is capable of ad-
dressing 4K bytes of memory directly.
3.1.4.1 Data ROM
All read-only data is physically stored in program
memory, which also accommodates the Program
Space. The program memory consequently con-
tains the program code to be executed, as well as
the constants and look-up tables required by the
application.
3.1.3 Readout Protection
The Program Memory in OTP, EPROM or ROM
devices can be protected against external readout
of memory by setting the Readout Protection bit in
the option bytes (Section 3.3 on page 16).
The Data Space locations in which the different
constants and look-up tables are addressed by the
processor core may be thought of as a 64-byte
window through which it is possible to access the
read-only data stored in OTP/EPROM.
In the EPROM parts, Readout Protection option
can be desactivated only by U.V. erasure that also
results in the whole EPROM context being erased.
3.1.4.2 Data RAM
The data space includes the user RAM area, the
accumulator (A), the indirect registers (X), (Y), the
short direct registers (V), (W), the I/O port regis-
ters, the peripheral data and control registers, the
interrupt option register and the Data ROM Win-
dow register (DRWR register).
Note: Once the Readout Protection is activated, it
is no longer possible, even for STMicroelectronics,
to gain access to the OTP or ROM contents. Re-
turned parts can therefore not be accepted if the
Readout Protection bit is set.
3.1.4 Data Space
3.1.5 Stack Space
Data Space accommodates all the data necessary
for processing the user program. This space com-
prises the RAM resource, the processor core and
peripheral registers, as well as read-only data
Stack space consists of six 12-bit registers which
are used to stack subroutine and interrupt return
addresses, as well as the current program counter
contents.
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