48GA004 datasheet(25/268 Pages) MICROCHIP

25 / 268 page

 2010 Microchip Technology Inc.

DS39881D-page 25

PIC24FJ64GA004 FAMILY

3.0

CPU

The PIC24F CPU has a 16-bit (data) modified Harvard

architecture with an enhanced instruction set and a

24-bit instruction word with a variable length opcode

field. The Program Counter (PC) is 23 bits wide and

addresses up to 4M instructions of user program

memory space. A single-cycle instruction prefetch

mechanism is used to help maintain throughput and pro-

vides predictable execution. All instructions execute in a

single cycle, with the exception of instructions that

change the program flow, the double-word move

(MOV.D) instruction and the table instructions. Over-

head-free program loop constructs are supported using

the REPEAT instructions, which are interruptible at any

point.

PIC24F devices have sixteen, 16-bit working registers

in the programmer’s model. Each of the working

registers can act as a data, address or address offset

a Software Stack Pointer for interrupts and calls.

The upper 32 Kbytes of the data space memory map

can optionally be mapped into program space at any

16K word boundary defined by the 8-bit Program Space

Visibility Page Address (PSVPAG) register. The program

to data space mapping feature lets any instruction

access program space as if it were data space.

The Instruction Set Architecture (ISA) has been

significantly enhanced beyond that of the PIC18, but

maintains an acceptable level of backward compatibil-

ity. All PIC18 instructions and addressing modes are

supported, either directly, or through simple macros.

Many of the ISA enhancements have been driven by

compiler efficiency needs.

The core supports Inherent (no operand), Relative,

Literal, Memory Direct and three groups of addressing

modes. All modes support Register Direct and various

addressing modes. Instructions are associated with

predefined addressing modes depending upon their

functional requirements.

For most instructions, the core is capable of executing

a data (or program data) memory read, a working reg-

ister (data) read, a data memory write and a program

(instruction) memory read per instruction cycle. As a

result, three parameter instructions can be supported,

allowing trinary operations (that is, A + B = C) to be

executed in a single cycle.

A high-speed, 17-bit by 17-bit multiplier has been

included to significantly enhance the core arithmetic

capability and throughput. The multiplier supports

Signed, Unsigned and Mixed mode, 16-bit by 16-bit or

8-bit by 8-bit, integer multiplication. All multiply

instructions execute in a single cycle.

The 16-bit ALU has been enhanced with integer divide

assist hardware that supports an iterative non-restoring

divide algorithm. It operates in conjunction with the

REPEAT

instruction looping mechanism and a selection

of iterative divide instructions to support 32-bit (or

16-bit), divided by 16-bit, integer signed and unsigned

division. All divide operations require 19 cycles to

complete but are interruptible at any cycle boundary.

The PIC24F has a vectored exception scheme with up

to 8 sources of non-maskable traps and up to 118 inter-

rupt sources. Each interrupt source can be assigned to

one of seven priority levels.

A block diagram of the CPU is shown in Figure 3-1.

3.1

Programmer’s Model

The programmer’s model for the PIC24F is shown in

Figure 3-2. All registers in the programmer’s model are

memory mapped and can be manipulated directly by

instructions. A description of each register is provided

in Table 3-1. All registers associated with the

programmer’s model are memory mapped.

Note:

This data sheet summarizes the features

of this group of PIC24F devices. It is not

intended to be a comprehensive reference

source. For more information, refer to the

“PIC24F

Family

Reference

Manual”

”Section 2. CPU”

(DS39703).

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