ST10R272L - MEMORY ORGANIZATION
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3.1.4
Special function registers
The functions of the CPU, the bus interface, the I/O ports and the on-chip peripherals are
controlled by Special Function Registers (SFRs). The SFRs are arranged in two areas of
512 bytes each. The first register block - the SFR area - is located in the 512 Bytes above the
internal RAM (00’FFFFh...00’FE00h), the second register block - the Extended SFR (ESFR)
area - is located in the 512 Bytes below the internal RAM (00’F1FFh...00’F000h).
Special function registers can be addressed via indirect and long, 16-bit addressing modes.
Using an 8-bit offset, together with an implicit base address, makes it possible to address
word SFRs and their respective low bytes. However, this does not work for the respective
high bytes!
Writing to any byte of an SFR causes the non-addressed complementary byte to be cleared!
The upper half of each register block is bit-addressable, so the respective control/status bits
can be directly modified or checked, using bit-addressing.
Identification registers are held in the SFR area.
When accessing registers in the ESFR area - using 8-bit addresses or direct bit addressing
- an extend register (EXTR) instruction is required to switch the short addressing mechanism
from the standard SFR area to the extended SFR area. This is not required for 16-bit and
Figure 7 Location of the PEC pointers
00’FCFE
H
00’FCFC
H
00’FCE2
H
00’FCE0
H
DSTP7
SRCP7
DSTP0
SRCP0
00’F600
H
00’FCDE
H
00’FCE0
H
00’FCFE
H
00’FD00
H
00’F5FE
H
Internal RAM
PEC source
&
destination
pointers