PIC16F627A datasheet(11/180 Pages) MICROCHIP

11 / 180 page

DS40044G-page 11

PIC16F627A/628A/648A

3.0

ARCHITECTURAL OVERVIEW

The high performance of the PIC16F627A/628A/648A

family can be attributed to a number of architectural

features commonly found in RISC microprocessors. To

begin with, the PIC16F627A/628A/648A uses a

Harvard architecture in which program and data are

accessed from separate memories using separate

busses. This improves bandwidth over traditional Von

Neumann architecture where program and data are

fetched from the same memory. Separating program

and data memory further allows instructions to be sized

differently than 8-bit wide data word. Instruction

opcodes are 14-bits wide making it possible to have all

single-word instructions. A 14-bit wide program mem-

ory access bus fetches a 14-bit instruction in a single

cycle. A two-stage pipeline overlaps fetch and execu-

tion of instructions. Consequently, all instructions (35)

execute in a single-cycle (200 ns @ 20 MHz) except for

program branches.

Table 3-1 lists device memory sizes (Flash, Data and

EEPROM).

TABLE 3-1:

DEVICE MEMORY LIST

The PIC16F627A/628A/648A can directly or indirectly

address its register files or data memory. All Special

Function Registers (SFR), including the program

counter, are mapped in the data memory. The

PIC16F627A/628A/648A have an orthogonal (symmet-

rical) instruction set that makes it possible to carry out

any operation, on any register, using any addressing

mode. This symmetrical nature and lack of ‘special

optimal situations’ makes programming with the

PIC16F627A/628A/648A simple yet efficient. In

addition, the learning curve is reduced significantly.

The PIC16F627A/628A/648A devices contain an 8-bit

ALU and working 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

otherwise mentioned, arithmetic operations are two’s

complement in nature. In two-operand instructions,

typically one operand is the working register

(W register). The other operand is 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 Borrow and Digit Borrow out bits,

respectively, in subtraction. See the SUBLW and SUBWF

instructions for examples.

A simplified block diagram is shown in Figure 3-1, and

a description of the device pins in Table 3-2.

Two types of data memory are provided on the

PIC16F627A/628A/648A

devices.

Nonvolatile

EEPROM data memory is provided for long term

storage of data, such as calibration values, look-up

table data, and any other data which may require

periodic updating in the field. These data types are not

lost when power is removed. The other data memory

provided is regular RAM data memory. Regular RAM

data memory is provided for temporary storage of data

during normal operation. Data is lost when power is

removed.

Device

Memory

Flash

Program

RAM

Data

EEPROM

Data

PIC16F627A

1024 x 14

224 x 8

128 x 8

PIC16F628A

2048 x 14

224 x 8

128 x 8

PIC16F648A

4096 x 14

256 x 8

PIC16LF627A

1024 x 14

224 x 8

128 x 8

PIC16LF628A

2048 x 14

224 x 8

128 x 8

PIC16LF648A

4096 x 14

256 x 8

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