only) are transferred.
鈥?/div>
DO
instruction
DOSTART, DOEND, DCOUNT shadows are
pushed on loop start, and popped on loop end.
When a byte operation is performed on a working reg-
ister, only the Least Significant Byte of the target regis-
ter is affected. However, a benefit of memory mapped
working registers is that both the Least and Most Sig-
nificant Bytes can be manipulated through byte wide
data memory space accesses.
SOFTWARE STACK POINTER/
FRAME POINTER
The dsPIC
庐
devices contain a software stack. W15 is
the dedicated software Stack Pointer (SP), and will be
automatically modified by exception processing and
subroutine calls and returns. However, W15 can be ref-
erenced by any instruction in the same manner as all
other W registers. This simplifies the reading, writing
and manipulation of the stack pointer (e.g., creating
stack frames).
Note:
In order to protect against misaligned
stack accesses, W15<0> is always clear.
W15 is initialized to 0x0800 during a Reset. The user
may reprogram the SP during initialization to any
location within data space.
W14 has been dedicated as a stack frame pointer as
defined by the
LNK
and
ULNK
instructions. However,
W14 can be referenced by any instruction in the same
manner as all other W registers.
2.2.2
STATUS REGISTER
The dsPIC core has a 16-bit STATUS register (SR), the
LS Byte of which is referred to as the SR Low byte
(SRL) and the MS Byte as the SR High byte (SRH).
See Figure 2-1 for SR layout.
SRL contains all the MCU ALU operation status flags
(including the Z bit), as well as the CPU Interrupt Prior-
ity Level status bits, IPL<2:0> and the Repeat Active
status bit, RA. During exception processing, SRL is
concatenated with the MS Byte of the PC to form a
complete word value which is then stacked.
The upper byte of the STATUS register contains the
DSP Adder/Subtracter status bits, the DO Loop Active
bit (DA) and the Digit Carry (DC) status bit.
2.2.3
PROGRAM COUNTER
The program counter is 23-bits wide; bit 0 is always
clear. Therefore, the PC can address up to 4M
instruction words.
DS70117C-page 14
Preliminary
铮?/div>
2004 Microchip Technology Inc.
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