33FJ128GP708 datasheet(11/90 Pages) MICROCHIP

11 / 90 page

Preliminary

DS70155C-page 9

dsPIC33F

3.2

Programmer’s Model

The programmer’s

model, shown in Figure 3-2,

consists of 16 x 16-bit working registers (W0 through

W15), 2 x 40-bit accumulators (ACCA and ACCB),

Status Register (SR), Data Table Page register

(TBLPAG), Program Space Visibility Page register

(PSVPAG), DO and REPEAT registers (DOSTART,

DOEND, DCOUNT and RCOUNT) and Program

Counter (PC). The working registers can act as data,

address or offset registers. All registers are memory

mapped. W0 is the W register for all instructions that

perform file register addressing.

Some of these registers have a shadow register

associated with them (see the legend in Figure 3-2).

The shadow register is used as a temporary holding

None of the shadow registers are accessible directly.

When a byte operation is performed on a working

mapped working registers is that both the Least and

Most Significant Bytes can be manipulated through

byte-wide data memory space accesses.

W15 is the dedicated software Stack Pointer (SP). It is

automatically modified by exception processing and

subroutine calls and returns. However, W15 can be

referenced 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).

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.

The Stack Pointer always points to the first available

free word and grows from lower addresses towards

higher addresses. It pre-decrements for stack pops

(reads) and post-increments for stack pushes (writes).

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