I2CCON datasheet(19/210 Pages) MICROCHIP

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DS70139G-page 19

dsPIC30F2011/2012/3012/3013

2.0

CPU ARCHITECTURE

OVERVIEW

This section is an overview of the CPU architecture of

the dsPIC30F. The core has a 24-bit instruction word.

The Program Counter (PC) is 23 bits wide with the

Least

Significant

bit

(LSb)

always

clear

(see

Section 3.1 “Program Address Space”). The Most

Significant bit (MSb) is ignored during normal program

execution, except for certain specialized instructions.

Thus, the PC can address up to 4M instruction words

of user program space. An instruction prefetch

mechanism helps maintain throughput. Program loop

constructs,

free

from

loop

count

management

overhead, are supported using the DO and REPEAT

instructions, both of which are interruptible at any point.

2.1

Core Overview

The working register array consists of 16 x 16-bit

registers, each of which can act as data, address or

offset registers. One working register (W15) operates

as a Software Stack Pointer for interrupts and calls.

The data space is 64 Kbytes (32K words) and is split

into two blocks, referred to as X and Y data memory.

Each block has its own independent Address Genera-

tion Unit (AGU). Most instructions operate solely

through the X memory, AGU, which provides the

appearance of a single unified data space. The

Multiply-Accumulate (MAC) class of dual source DSP

instructions operate through both the X and Y AGUs,

splitting the data address space into two parts (see

Section 3.2 “Data Address Space”). The X and Y

data space boundary is device specific and cannot be

altered by the user. Each data word consists of 2 bytes

and most instructions can address data either as words

or bytes.

Two ways to access data in program memory are:

• The upper 32 Kbytes of data space memory can

be mapped into the lower half (user space) of

program space at any 16K program word

boundary, defined by the 8-bit Program Space

Visibility Page register (PSVPAG). Thus any

instruction can access program space as if it were

data space, with a limitation that the access

requires an additional cycle. Only the lower 16

bits of each instruction word can be accessed

using this method.

• Linear indirect access of 32K word pages within

program space is also possible using any working

Table read and write instructions can be used to

access all 24 bits of an instruction word.

Overhead-free circular buffers (Modulo Addressing)

are supported in both X and Y address spaces. This is

primarily intended to remove the loop overhead for

DSP algorithms.

The X AGU also supports Bit-Reversed Addressing on

destination effective addresses to greatly simplify input

or output data reordering for radix-2 FFT algorithms.

Refer to Section 4.0 “Address Generator Units” for

details on Modulo and Bit-Reversed Addressing.

The core supports Inherent (no operand), Relative,

Literal, Memory Direct, Register Direct, Register

Indirect, Register Offset and Literal Offset Addressing

modes. Instructions are associated with pre-defined

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

program (instruction) memory read per instruction

cycle. As a result, 3 operand instructions are

supported, allowing C = A+B operations to be exe-

cuted in a single cycle.

A DSP engine has been included to significantly

enhance the core arithmetic capability and throughput.

It features a high-speed 17-bit by 17-bit multiplier, a

40-bit ALU, two 40-bit saturating accumulators and a

40-bit

bidirectional

barrel

shifter.

Data

the

accumulator or any working register can be shifted up

to 15 bits right, or 16 bits left in a single cycle. The DSP

instructions

operate

seamlessly

with

all

other

instructions and have been designed for optimal

real-time performance. The MAC class of instructions

can concurrently fetch two data operands from memory

while multiplying two W registers. To enable this

concurrent fetching of data operands, the data space

has been split for these instructions and linear is for all

others. This has been achieved in a transparent and

flexible manner, by dedicating certain working registers

to each address space for the MAC

class of

instructions.

Note:

This data sheet summarizes features of

this group of dsPIC30F devices and is not

intended to be a complete reference

source. For more information on the CPU,

peripherals,

descriptions

and

general device functionality, refer to the

“dsPIC30F Family Reference Manual”

(DS70046). For more information on the

device instruction set and programming,

refer to the “16-bit MCU and DSC

Programmer’s

Reference

Manual”

(DS70157).

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