PIC16F57-ISLASHSP datasheet(9/88 Pages) MICROCHIP

9 / 88 page

DS41213D-page 7

PIC16F5X

2.0

ARCHITECTURAL OVERVIEW

The high performance of the PIC16F5X family can be

attributed to a number of architectural features

commonly found in RISC microprocessors. To begin

with, the PIC16F5X uses a Harvard architecture in

which program and data are accessed on separate

buses. This improves bandwidth over traditional von

Neumann architecture where program and data are

fetched on the same bus. Separating program and data

memory further allows instructions to be sized differ-

ently than the 8-bit wide data word. Instruction opcodes

are 12-bits wide, making it possible to have all single-

word instructions. A 12-bit wide program memory

access bus fetches a 12-bit instruction in a single cycle.

A two-stage pipeline overlaps fetch and execution of

instructions. Consequently, all instructions (33) execute

in a single cycle except for program branches.

The

PIC16F54

addresses

512 x 12

program

memory, the PIC16F57 and PIC16F59 addresses

2048 x 12 of program memory. All program memory is

internal.

The PIC16F5X can directly or indirectly address its

Registers (SFR), including the program counter, are

mapped in the data memory. The PIC16F5X has a

highly orthogonal (symmetrical) instruction set that

makes it possible to carry out any operation on any reg-

ister using any Addressing mode. This symmetrical

nature and lack of ‘special optimal situations’ make pro-

gramming with the PIC16F5X simple, yet efficient. In

addition, the learning curve is reduced significantly.

The PIC16F5X device contains an 8-bit ALU and work-

ing register. The ALU is a general purpose arithmetic

unit. It performs arithmetic and Boolean functions

between data in the working register and any register

file.

The ALU is 8-bits wide and capable of addition,

subtraction, shift and logical operations. Unless other-

wise mentioned, arithmetic operations are two's

complement in nature. In two-operand instructions,

typically one operand is the W (working) register. The

other operand is either a file register or an immediate

constant. In single operand instructions, the operand is

either the W register or a file register.

The W register is an 8-bit working register used for ALU

operations. It is not an addressable register.

Depending on the instruction executed, the ALU may

affect the values of the Carry (C), Digit Carry (DC) and

Zero (Z) bits in the STATUS Register. The C and DC

bits operate as a borrow and digit borrow out bit,

respectively, in subtraction. See the SUBWF and ADDWF

instructions for examples.

A simplified block diagram is shown in Figure 2-1 with

the corresponding device pins described in Table 2-1

(for PIC16F54), Table 2-2 (for PIC16F57) and

Table 2-3 (for PIC16F59).

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