unit-i - fmcetfmcet.in/eee/ee6502(r-13)_uw.pdf8085 microprocessor architecture ... memory label...

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Building Blocks of Processor Systems

MEMORY

DATAPATH

CONTROL

INPUT-OUTPUT

CPU

3

Processor System Architecture

The typical processor system consists of:

� CPU (central processing unit)

� ALU (arithmetic-logic unit)

� Control Logic

� Registers, etc…

� Memory

� Input / Output interfaces

Interconnections between these units:

� Address Bus

� Data Bus

� Control Bus

4

Bus and CPU

Bus: A shared group of wires used for communicating

signals among devices

• address bus: the device and the location within the

device that is being accessed

• data bus: the data value being communicated

• control bus: describes the action on the address and data

buses

CPU: Core of the processor, where instructions are executed

• High-level language: a = b + c

• Assembly language: add r1 r2 r3

• Machine language: 0001001010111010101

5

Memory and I/O

Memory:Where instructions (programs) and data are stored

• Organized in arrays of locations (addresses), each storing

one byte (8 bits) in general

• A read operation to a particular location always returns the

last value stored in that location

I/O devices: Enable system to interact with the world

• Device interface (a.k.a. controller or adapter) hardware

connects actual device to bus

• The CPU views the I/O device registers just like

memory that can be accessed over the bus. However,

I/O registers are connected to external wires, device

control logic, etc.

• Reads may not return last value written

• Writes may have side effects

6

8085 Microprocessor Architecture

Now we will examine these components more closely

by using the Intel 8085 microprocessor architecture

as an example:

UNIT-I

EE6502 Microprocessor & Microcontroller

2

7

The 8085 Bus Structure

The 8-bit 8085 CPU (or MPU – Micro Processing Unit)

communicates with the other units using a 16-bit address

bus, an 8-bit data bus and a control bus.

8


Address Bus

� Consists of 16 address lines: A0 – A15

� Operates in unidirectional mode: The address

bits are always sent from the MPU to peripheral

devices, not reverse.

� 16 address lines are capable of addressing a

total of 216 = 65,536 (64k) memory locations.

� Address locations: 0000 (hex) – FFFF (hex)

9


Data Bus

� Consists of 8 data lines: D0 – D7

� Operates in bidirectional mode: The data bits are

sent from the MPU to peripheral devices, as well

as from the peripheral devices to the MPU.

� Data range: 00 (hex) – FF (hex)

Control Bus

� Consists of various lines carrying the control

signals such as read / write enable, flag bits.

10

The 8085: CPU Internal Structure

The internal architecture of the 8085 CPU is

capable of performing the following operations:

� Store 8-bit data (Registers, Accumulator)

� Perform arithmetic and logic operations (ALU)

� Test for conditions (IF / THEN)

� Sequence the execution of instructions

� Store temporary data in RAM during execution

11


Simplified block diagram

12

The 8085: Registers

3

13


Registers

� Six general purpose 8-bit registers: B, C, D, E, H, L

� They can also be combined as register pairs to

perform 16-bit operations: BC, DE, HL

� Registers are programmable (data load, move, etc.)

Accumulator

� Single 8-bit register that is part of the ALU !

� Used for arithmetic / logic operations – the result is

always stored in the accumulator.

14


Flag Bits

� Indicate the result of condition tests.

� Carry, Zero, Sign, Parity, etc.

� Conditional operations (IF / THEN) are executed

based on the condition of these flag bits.

Program Counter (PC)

� Contains the memory address (16 bits) of the

instruction that will be executed in the next step.

Stack Pointer (SP)

15

Example: Memory Read Operation

16

Example: Instruction Fetch Operation

� All instructions (program steps) are stored in memory.

� To run a program, the individual instructions must

be read from the memory in sequence, and executed.

� Program counter puts the 16-bit memory address of the

instruction on the address bus

� Control unit sends the Memory Read Enable signal to

access the memory

� The 8-bit instruction stored in memory is placed on the data

bus and transferred to the instruction decoder

� Instruction is decoded and executed

17


18


4

19

8085 Functional Block Diagram

02.ADDITION OF TWO 8 BIT NUMBERS

(b) BY DIRECT ADDRESSING MODE

MEMORY LABEL MNEMONICS OPCODE COMMENTS

A000 START LDA B000 3A LOAD DATA TO ACC

A001 00

A002 B0

A003 MOV B,A 47 MOVE B�A

A004 LDA B001 3A LOAD DATA TO ACC

A005 01

A006 B0

A007 ADD B 80 ADD B TO ACC A�A+B

A008 STA B002 32 STORE ACC TO B002

A009 02

A00A B0

A00B STOP HLT 76 HALT


(a) BY IMMEDIATE ADDRESSING MODE


A000 START MVI A,07 3E MOV�07

A001 07

A002 ADI 08 C6 ADD IMMEDIATE A�A+08

A003 08

A004 STA B000 32 STORE B�A

A005 00

A006 BO

A007 STOP HLT 76 HALT

UNIT-II


(C) BY INDIRECT ADDRESSING MODE


A000 START LXI H,B000 21 LOAD DATA IN HL PAIR

A001 00

A002 B0

A003 MOV A,M 7E MOVE A�M

A004 INX H 23 INCREMENT H

A005 ADD M 86 ADD A�A+M


A007 MOV M,A 77 MOVE M�A



(d) ADDITION WITH CARRY


A000 START MVI C,00 0E,00 (C)�00

A002 LDA 8050 3A,50,80 ACC�(8050)

A005 MOV B,A 47 (B)�A

A006 LDA 8051 3A,51,80 ACC�(8051)

A009 ADD B 80 A�(A)+(B)

A00A STA 8052 32,53,80 (8052)�(A)

A00D MVI A,00 3E,00 (A)�00

A00F STA 8053 32,53,80 (8053)�(A)

A012 JNC A01A D2,10,A0 JUMP TO AO1A IF ZERO CARRY

A015 INR C 0C INCREMENT C

A016 MOV A,C 79 (C)�(A)

A017 JNC STA 8053 32,53,80 (A)�(8053)

A01A STOP HLT 76 HALT

02.SUBTRACTION OF TWO 8 BIT NUMBERS

(e) BY IMMEDIATE ADDRESSING MODE


A000 START MVI A,09 3E MOVE A�09

A001 09

A002 SUI 08 D6 SUB IMMEDIATELY BY 08 A�A-08

A003 08

A004 STA B000 32 STORE A TO B000

A005 00

A006 B0



(f) BY DIRECT ADDRESSING MODE


A000 START LDA B000 3A LOAD DATA TO ACC

A001 00

A002 B0

A003 MOV B,A 47 MOVE B�A

A004 LDA B001 3A LOAD DATA TO ACC

A005 01

A006 B0

A007 SUB B 90 SUBTRACT A�A-B

A008 STA B002 32 STORE ACC TO B002

A009 02

A00A B0

A00B STOP 76 HLT HALT


(g) BY INDIRECT ADDRESSING MODE


A000 START LXI H,B000 21 LOAD DATA IN HL PAIR

A001 00

A002 B0

A003 MOV A,M 7E MOVE A�M


A005 SUB M 96 SUB A�A-M


A007 MOV M,A 77 MOVE M�A


03(a). MULTIPLICATION OF TWO 8 BIT NUMBERS


A000 START LXI D,0000 11,00,00 INITIALISE DE PAIR

A003 LXI H,0000 21,00,00 INITIALISE HL PAIR

A006 LDA A050 3A,50,A0 LOAD ACC WITH ADD

A009 MOV C,A 4F MOVE THE CONTENT FROM C�A

A00A LDA A051 3A,51,A0 LOAD ACC WITH ADD

A00D MOV E,A 5F MOVE E�A

A00E SKIP DAD D 19 ADD THE CONTENT

A00F DCR C 0D DECREMRNT THE COUNT

A010 JNZ SKIP CZ,0E,AO CHECK FOR ZERO

A013 SHLD A052 22,52,A0 STORE THE RESULT

A016 STOP HLT 76 STOP

03(b).DIVISION OF TWO 8 BIT NUMBERS


A000 START MVI A,06 3E,06 A�06

A002 MVI B,02 06,02 B�02

A004 MVI C,00 0E,00 C�00

A006 L1 INR C 0C C�C+1

A007 SUB B 90 B�A-B

A008 JNZ L1 CZ,06,A0 CHECK FOR ZERO

A00B MOV A,C 79 A�C

A00C STA 8050 32,50,80 STORE THE RESULT

A00F STOP HLT 76 HALT

04(a)ADDITION OF TWO 16 BIT NUMBERS


A000 START MVI B,00 06,00 B�00

A002 LHLD A050 2A,50,A0 LOAD A050 IN HL PAIR

A005 XCHG EB EXCHANGE CONTENTS OF HL AND DE

REGISTER PAIR

A006 LHLD A052 2A,52,A0 LOAD A052 IN HL PAIR

A009 DAD D 19 HL�HL+DE

A00A SHLD A054 22,54,40 STORE THE SUM

A00D JNC SKIP D2,11,AD SKIP IF CARRY=0

A010 INR B 04 B�B+1

A011 SKIP MOV A,B 78 A�B

A012 STA A056 32,56,A0 STORE THE CARRY

A015 STOP HLT 76 STOP

04(b)SUBTRACTION OF TWO 16 BIT NUMBERS


A000 START LHLD 8050 2A,50,80 HL�(8050)


REGISTER PAIR

A004 LHLD 8052 2A,52,80 HL�(8052)

A007 MOV A,L 7D A�L

A008 SUB E 93 A�A-E

A009 MOV L,A 6F L�A

A00A MOV A,H 7C A�H

A00B SUB D 92 A�A-D

A00C MOV H,A 67 H�A

A00D SHLD 8054 22,50,80 (8054),--HL


05(a) MULTIPLICATION OF A 16 BIT NUMBER BY 8 BIT NUMBER


A000 START LHLD 8050 2A,50,80 HL�(8050)


REGISTER PAIR

A004 LXI H,0000 21.00.00 LOAD DATA IN HL PAIR

A007 MVI B,11 06.11 MOVE IMMEDIATELY B�11

A009 MVI C,00 0E,00 MOVE IMMEDIATELY L�00

A00B L2 DAD D 19 HL�HL+DE

A00C JNC L1 D2,10.A0 JUMP ON NO CARRY TO L1

A00F INR C 0C C�C+1

A010 L1 DCR B 05 B�B-1

A011 JNZ L2 C2,03,A0 JUMP ON NO ZERO TO L2

A014 SHLD 8060 22,60,80 STORE IN HL PAIR

A017 MOV A,C 79 A�C

A018 STA 8062 32,62,80 STORE VALUE


05(b) DIVISION OF A 16 BIT NUMBER BY 16 BIT NUMBER


8050 START LHLD 8050 2A,50,80 HL�(8050)

8052 XCHG EB EXCHANGE CONTENTS OF HL AND DE

REGISTER PAIR

8054 LHLD 8002 2A,02,80 HL�(8052)

8057 LXI B,000 01,00,00 LOAD B=0000

805A L1 INX B 03 INCREMENT BC PAIR

805B MOV A,L 7D A�L

805C SUB E 93 SUBTRACT E

805D MOV L,A 6F L�A

805E MOV A,H 7C A�H

805F SBB D 9A SUBTRACT WITH BORROW D

8060 MOV H,A 67 H�A

8061 JNC L1 D2,5A,80 JUMP ON NO CARRY TO L1

8064 DAD D 19 HL�HL+DE

8065 DCX B 0B DECREMENT BC PAIR

8066 SHLD 8004 22,04,80 STORE IN HL PAIR

8069 MOV H,B 60 H�B

806A MOV L,C 69 L�C

806B SHLD 8006 22,06,80 STORE IN HL PAIR

806C STOP HLT 76 HALT

06.CODE CONVERSION

(a)BCD TO BINARY


A000 START LDA 8050 3A,50,80 LOAD ACC�8050

A003 MOV E,A 5F MOVE E�A

A004 ANI F0 E6,FO IMMEDIATE AND

A006 RLC 07 ROTATE LEFT




A00A MOV B,A 47 B�A

A00B XRA A AF XOR

A00C MVI C,A 0E,0A C�0A

A00E REP ADD B 80 ADD B

A00F DCR C 0D DECREMENT C

A010 JNZ REP CE,0E,A0 JUMP ON NO ZERO TO REP

A013 MOV B,A 47 B�A

A014 MOV A,E 7B A�E

A015 ANI OF E6,0F IMMEDIATE AND

A017 ADD B 80 ADD B

A018 STA 8051 32,51,80 STORE THE RESULT

A01B STOP HLT 76 HALT

06.CODE CONVERSION

(b) BINARY TO BCD


A000 START MVI E,00 1E,00 MOVE IMMEDIATELY E�00

A002 MOV D,E 53 MOVE D�E

A003 LDA 8050 3A,50,80 LOAD ACCUMULATOR WITH 8050

A006 HUND CPI 64 FE,64 COMPLIMENT IMMEDIATELY

A008 JC TEN DA,11,A0 JUMP WITH CARRY TO TEN

A00B SUI 64 D6,64 SUBTARCT IMMEDIATELY

A00D INR E 1C INCREMENT

A00E JUMP HUND C3,06,A0 JUMP TO HUND

A011 TEN CPI 0A FE,0A COMPLIMENT IMMEDIATELY

A013 JC UNIT DA,1C,A0 JUMP WITH CARRY TO UNIT

A016 SUI 0A D6,0A SUBTARCT IMMEDIATELY

A018 INR D 14 INCREMENT

A019 JMP TEN C3,11,A0 JUMP TO TEN

A01C UNIT MOV C,A 4F MOVE C�A

A01D MOV A,D 7A MOVE A�D

A01E RLC 07 ROTATE LEFT

A01F RLC 07 ROTATE LEFT



A022 ADD C 81 ADD A�A+C

A023 STA 8051 32,51,80 STORE TO 8051

A026 MOV A,E 7B MOVE A�E

A027 STA 8052 32,52,80 STORE TO 8052

A02A STOP HLT 76 HALT

06.CODE CONVERSION

(C)HEX TO ASCII


8000 START LDA 8050 3A,50,80 LOAD ACC WITH DATA

8003 CPI 0A FE,0A COMPUTE IMMEDIATELY 0A

8005 JC L1 DA,0A,80 JUMP IF CARRY TO L1

8008 ADI 07 C6,07 ADD IMMEDIATE 07

800A L1 ADI 30 C6,30 ADD IMMEDIATELY 30

800C STA 8051 32,51,80 STORE THE RESULT

800F STOP HLT 76 HALT

06.CODE CONVERSION

(d)ASCII TO HEX


A000 START LDA 8050 3A,50,80 LOAD ACC WITH DATA

A003 SUI 30 D6,30 SUB IMMEDIATELY

A005 CPI 0A FE,0A COMPUTE IMMEDIATELY 0A

A007 JC L1 DA,0C,80 JUMP IF CARRY TO L1

A00A SUI 07 D6,07 SUB IMMEDIATELY

A00C L1 STA 8051 32,51,80 STORE THE RESULT

A00F STOP HLT 76 HALT

07.SORTING OF NUMBERS

(a)ASCENDING ORDER


8000 START MVI C,05 0E,05 C�05

8002 L4 LXI H,8050 21,50,80 LOAD ADDRESS IN HL

8005 MVI D,05 16,05 D�05

8007 MOV A,M 7E A�H

8008 L3 INX H 23 INCREMENT HL

8009 MOV B,M 46 B�H

800A CMP B B8 COMPARE B WITH A

800B JNC L1 D2,14,80 JUMP ON NO CARRY

800E DCX H 2B DECREMENT HL

800F MOV M,A 77 M�A

8010 MOV A,B 78 A�B

8011 JMP L2 C3,16,80 UNCONDITIONAL JUMP

8014 L1 DCX H 2B DECREMENT HL

8015 MOV M,B 70 H�B


8017 DCR D 15 DECREMENT D

8018 JNZ L3 C2,08,80 JUMP ON NO ZERO

801B MOV M,A 77 M�A

801C DCR C 0D DECREMENT C

801D JNZ L4 C2,02,80 JUMP ON NO ZERO

8020 STOP HLT 76 HALT

07.SORTING OF NUMBERS

(b)DESCENDING ORDER


8000 START MVI C,05 0E,05 C�05

8002 L4 LXI H,8050 21,50,80 LOAD ADDRESS IN HL

8005 MVI D,05 16,05 D�05

8007 MOV A,M 7E A�H


8009 MOV B,M 46 B�H

800A CMP B B8 COMPARE B WITH A

800B JC L1 D2,14,80 JUMP ON NO CARRY

800E DCX H 2B DECREMENT HL

800F MOV M,A 77 M�A

8010 MOV A,B 78 A�B

8011 JMP L2 C3,16,80 UNCONDITIONAL JUMP

8014 L1 DCX H 2B DECREMENT HL

8015 MOV M,B 70 H�B


8017 DCR D 15 DECREMENT D

8018 JNZ L3 C2,08,80 JUMP ON NO ZERO

801B MOV M,A 77 M�A

801C DCR C 0D DECREMENT C

801D JNZ L4 C2,02,80 JUMP ON NO ZERO


08.MESSAGE DISPLAY

SINGLE CHARACTER


8000 MVI A,90 3E,90 CONTROL WORD

8002 OUT 31 DB,31

8004 MVI A,67 3E,67 DATA

8006 OUT 30 D3,30

8008 HLT 76 HALT

08.MESSAGE DISPLAY

MULTIPLE CHARACTER


8000 MVI A,90 3E,90 CONTROL

WORD

8002 OUT 31 DB,31

8004 MVI A,67 3E,67 DATA 1

8006 OUT 30 D3,30

8008 MVI A,93 3E,93 DATA 2

800A OUT 30 D3,30

800C MVI A,97 3E,97 DATA 3

800E OUT 30 D3,30

8010 MVI A,97 3E,97 DATA 4

8012 OUT 30 D3,30

8014 MVI A,60 3E,60 DATA 5

8016 OUT 30 D3,30

8018 MVI A,97 3E,97 DATA 6

801A 0UT30 D3,30

801C HLT 76 HALT

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1

Contents

• Introduction

• Block Diagram and Pin Description of the 8051

• Instruction format and addressing modes

• Interrupt structure

• Timer

• I/O ports

• Serial communication

MICRO CONTROLLER 8051

III UNIT

2

The necessary tools for a

microprocessor/controller

• CPU: Central Processing Unit

• I/O: Input /Output

• Bus: Address bus & Data bus

• Memory: RAM & ROM

• Timer

• Interrupt

• Serial Port

• Parallel Port

CPU

General-

Purpose

Micro-

processor

RAM ROM I/O

PortTimer

Serial

COM

Port

Data Bus

Address Bus

General-Purpose Microprocessor System

Microprocessors:

• CPU for Computers

• No RAM, ROM, I/O on CPU chip itself

• Example覲Intel’s x86, Motorola’s 680x0

Many chips on mother’s board

General-purpose microprocessor

3

RAM ROM

I/O

PortTimer

Serial

COM

PortMicrocontroller

CPU

• A smaller computer

• On-chip RAM, ROM, I/O ports...

• Example覲Motorola’s 6811, Intel’s 8051, Zilog’s Z8 and PIC 16X

A single chip

Microcontroller :

Microprocessor

• CPU is stand-alone, RAM,

ROM, I/O, timer are separate

• designer can decide on the

amount of ROM, RAM and

I/O ports.

• expansive

• versatility

• general-purpose

Microcontroller

• CPU, RAM, ROM, I/O and

timer are all on a single chip

• fix amount of on-chip ROM,

RAM, I/O ports

• for applications in which cost,

power and space are critical

• single-purpose

Microprocessor vs. Microcontroller

4

• Embedded system means the processor is embedded into that

application.

• An embedded product uses a microprocessor or microcontroller

to do one task only.

• In an embedded system, there is only one application software

that is typically burned into ROM.

• Example覲printer, keyboard, video game player

Embedded System

1. meeting the computing needs of the task efficiently and cost

effectively

• speed, the amount of ROM and RAM, the number of I/O

ports and timers, size, packaging, power consumption

• easy to upgrade

• cost per unit

2. availability of software development tools

• assemblers, debuggers, C compilers, emulator, simulator,

technical support

3. wide availability and reliable sources of the microcontrollers.

Three criteria in Choosing a Microcontroller

5

Block Diagram

CPU

On-chip

RAM

On-chip

ROM for

program

code

4 I/O Ports

Timer 0

Serial

PortOSC

Interrupt

Control

External interrupts

Timer 1

Timer/Counter

Bus

Control

TxD RxDP0 P1 P2 P3

Address/Data

Counter

Inputs

Sunday, February 17,

2008

Mahdi Hassanpour

Feature 8051 8052 8031

ROM (program space in bytes) 4K 8K 0K

RAM (bytes) 128 256 128

Timers 2 3 2

I/O pins 32 32 32

Serial port 1 1 1

Interrupt sources 6 8 6

Comparison of the 8051 Family Members

6

Pin Description of the 8051Pin Description of the 8051

1

23

45

6

78

91011

1213

1415

161718

1920

40

3938

3736

35

3433

323130

2928

2726

252423

2221

P1.0P1.1P1.2

P1.3P1.4

P1.5

P1.6P1.7

RST(RXD)P3.0(TXD)P3.1

(T0)P3.4(T1)P3.5

XTAL2

XTAL1GND

(INT0)P3.2

(INT1)P3.3

(RD)P3.7(WR)P3.6

VccP0.0(AD0)P0.1(AD1)

P0.2(AD2)P0.3(AD3)

P0.4(AD4)

P0.5(AD5)P0.6(AD6)

P0.7(AD7)

EA/VPPALE/PROG

PSENP2.7(A15)

P2.6(A14)P2.5(A13)P2.4(A12)

P2.3(A11)

P2.2(A10)P2.1(A9)P2.0(A8)

8051

(8031)

7

Pins of 8051襦襦襦襦1/4襤襤襤襤

• Vcc襦pin 40襤覲– Vcc provides supply voltage to the chip.

– The voltage source is +5V.

• GND襦pin 20襤覲ground

• XTAL1 and XTAL2襦pins 19,18襤

Figure (a). XTAL Connection to 8051Figure (a). XTAL Connection to 8051

C2

30pF

C1

30pF

XTAL2

XTAL1

GND

� Using a quartz crystal oscillator

� We can observe the frequency on the XTAL2 pin.

8

Example :

Find the machine cycle for

(a) XTAL = 11.0592 MHz

(b) XTAL = 16 MHz.

Solution:

(a) 11.0592 MHz / 12 = 921.6 kHz;

machine cycle = 1 / 921.6 kHz = 1.085 µs

(b) 16 MHz / 12 = 1.333 MHz;

machine cycle = 1 / 1.333 MHz = 0.75 µs


• RST襦pin 9襤覲reset

– It is an input pin and is active high襦normally low襤.

• The high pulse must be high at least 2 machine cycles.

– It is a power-on reset.

• Upon applying a high pulse to RST, the

microcontroller will reset and all values in registers

will be lost.

• Reset values of some 8051 registers �

9

Figure (b). Power-On RESET Circuit

30 pF

30 pF

8.2 K

10 uF

+

Vcc

11.0592 MHz

EA/VPP

X1

X2

RST

31

19

18

9


• /EA襦pin 31襤覲external access

– There is no on-chip ROM in 8031 and 8032 .

– The /EA pin is connected to GND to indicate the code

is stored externally.

– /PSEN 襠 ALE are used for external ROM.

– For 8051, /EA pin is connected to Vcc.

– “/” means active low.

• /PSEN襦pin 29襤覲program store enable

– This is an output pin and is connected to the OE pin of

the ROM.

10


• ALE襦pin 30襤覲address latch enable

– It is an output pin and is active high.

– 8051 port 0 provides both address and data.

– The ALE pin is used for de-multiplexing the address and data by connecting to the G pin of the 74LS373 latch.

• I/O port pins

– The four ports P0, P1, P2, and P3.

– Each port uses 8 pins.

– All I/O pins are bi-directional..

Pins of I/O Port

• The 8051 has four I/O ports

– Port 0 襦pins 32-39襤覲P0襦P0.0譌P0.7襤– Port 1襦pins 1-8襤覲P1襦P1.0譌P1.7襤– Port 2襦pins 21-28襤覲P2襦P2.0譌P2.7襤– Port 3襦pins 10-17襤覲P3襦P3.0譌P3.7襤– Each port has 8 pins.

• Named P0.X 襦X=0,1,...,7襤, P1.X, P2.X, P3.X

• Ex覲P0.0 is the bit 0襦LSB襤of P0

• Ex覲P0.7 is the bit 7襦MSB襤of P0

• These 8 bits form a byte.

• Each port can be used as input or output (bi-direction).

11

Hardware Structure of I/O Pin

• Each pin of I/O ports

– Internal CPU bus覲communicate with CPU

– A D latch store the value of this pin

• D latch is controlled by “Write to latch”

– Write to latch覿1覲write data into the D latch

– 2 Tri-state buffer覲�

• TB1: controlled by “Read pin”

– Read pin覿1覲really read the data present at the pin

• TB2: controlled by “Read latch”

– Read latch覿1覲read value from internal latch

– A transistor M1 gate

• Gate=0: open

• Gate=1: close

D Latch:

12

A Pin of Port 1

8051 IC

D Q

Clk Q

Vcc

Load(L1)

Read latch

Read pin

Write to latch

Internal CPU

bus

M1

P1.X

pinP1.X

TB1

TB2

P0.x

Writing “1” to Output Pin P1.X

D Q

Clk Q

Vcc

Load(L1)

Read latch

Read pin

Write to latch

Internal CPU

bus

M1

P1.X

pinP1.X

8051 IC

2. output pin is

Vcc1. write a 1 to the pin

1

0 output 1

TB1

TB2

13

Writing “0” to Output Pin P1.X

D Q

Clk Q

Vcc

Load(L1)

Read latch

Read pin

Write to latch

Internal CPU

bus

M1

P1.X

pinP1.X

8051 IC

2. output pin is

ground1. write a 0 to the pin

0

1 output 0

TB1

TB2

Reading “High” at Input Pin

D Q

Clk Q

Vcc

Load(L1)

Read latch

Read pin

Write to latch

Internal CPU bus

M1

P1.X pin

P1.X

8051 IC

2. MOV A,P1

external pin=High1. write a 1 to the pin MOV

P1,#0FFH

1

0

3. Read pin=1 Read latch=0

Write to latch=1

1

TB1

TB2

14

Reading “Low” at Input Pin

D Q

Clk Q

Vcc

Load(L1)

Read latch

Read pin

Write to latch

Internal CPU bus

M1

P1.X pin

P1.X

8051 IC

2. MOV A,P1

external pin=Low1. write a 1 to the pin

MOV P1,#0FFH

1

0

3. Read pin=1 Read latch=0

Write to latch=1

0

TB1

TB2

Other Pins

• P1, P2, and P3 have internal pull-up resisters.

– P1, P2, and P3 are not open drain.

• P0 has no internal pull-up resistors and does not connects to Vcc inside the 8051.

– P0 is open drain.

– Compare the figures of P1.X and P0.X. �

• However, for a programmer, it is the same to program P0, P1, P2 and P3.

• All the ports upon RESET are configured as output.

15

A Pin of Port 0

8051 IC

D Q

Clk Q

Read latch

Read pin

Write to latch

Internal CPU

bus

M1

P0.X

pinP1.X

TB1

TB2

P1.x

Port 0 with Pull-Up Resistors

P0.0P0.1P0.2P0.3P0.4P0.5P0.6P0.7

DS5000

8751

8951

Vcc10 K

Port

0

PERIPHERAL INTERFACING -

IV UNIT

MICROPROCESSOR AND

MICROCONTROLLER

� Introduction

� 8255 is a widely used programmable, parallel I/O device

�Can be programmed to transfer data under various conditions,from simple I/O to interrupt I/O

�Has 24 I/O pins that can be grouped in two 8 bit parallel ports: A and B, with the remaining eight bits as port C.

�The 8 bits of port C can be used as individual bits or be grouped in two 4-bit ports: CUPPER(CU) and CLOWER(CL)

Port ACUCL

Port B

8255 Programmable Peripheral

Interface

2/17/2008

• Two Modes

– Bit Set/Reset (BSR) mode is used to set or reset the bits in

port C

– I/O mode

• Mode 0

• Mode 1

• Mode 2

�In mode 0 all ports function as simple I/O ports

�Mode 1 is a handshake mode whereby ports A and/or B

use bits from port C as handshake signals.

� Handshake mode (two types of I/O data transfer)

status check & interrupt

� In Mode 2, port A can be set up for bidirectional data

transfer using handshake signals from port C and port B

can be set up in either Mode 0 or Mode1.

D7 D6 D5 D4 D3 D2 D1 D0

0/1

Modes of 8255

BSR Mode

(Bit set/Reset)

For Port C

No effect on

I/O mode

I/O Mode

Mode 0

Simple I/O

For ports

A,B and C

Mode 1

Handshake I/O for

ports A and/or B

Port C bits

are used for

handshake

Mode 2

Bidirectional

data bus for

port A

Port B either

in Mode 0 or 1

Port C bits are

used for handshake

Pin Configuration

Signals of 8255

� It has a 40 pins of 4 groups.

1. Data bus buffer

2. Read Write control logic

3. Group A and Group B controls

4. Port A, B and C

� Data bus buffer: This is a tristate bidirectional buffer used to interface the 8255 to system data bus. Data is transmitted or received by the buffer on execution of

input or output instruction by the CPU.

� Read/Write control logic: This unit accepts control signals ( RD , WR ) and also inputs from address bus and issues commands to individual group of control

� blocks ( Group A, Group B).2/

8255 block diagram

2/17/2008

RD(active low): Read signal enables the read operation.

When this signal is low, the MPU reads data from a selected

I/O port of the 8255

WR(active low): Write control signal enables the write

operation. When this signal is low, the MPU writes into a

selected I/O port or the control register

RESET(active high): This signal clears the control

register and sets all ports in the input mode.

CS,A0 and A1: Device select signals: chip select is

connected to a decoded address and A0 and A1 are generally

connected to MPU address lines respectively

• The CS signal is the master chip select & A1 andA0 specify one

of the I/O ports

CS A1 A0 Selected

0 0 0 Port A

0 0 1 Port B

0 1 0 Port C

0 1 1 Control

Register

1 X X 8255 is not

selected

• Group A and Group B controls : These block receive control

from the CPU and issues commands to their respective ports.

• Group A - PA and PCU ( PC7 –PC4)

• Group B – PB and PCL ( PC3 – PC0)

• Control word register can only be written into & no read

operation of the CW register is allowed.

a) Port A: This has an 8 bit latched/buffered O/P and 8 bit input

latch. It can be programmed in 3 modes – mode 0, mode 1,

mode 2.

b) Port B: This has an 8 bit latched / buffered O/P and 8 bit input

latch. It can be programmed in mode 0, mode1.

c) Port C : This has an 8 bit latched input buffer and 8 bit out put

latched/buffer. This port can be divided into two 4 bit ports

and can be used as control signals for port A

and port B. it can be programmed in mode 0.

2/17/2008

Expanded version of the control logic

and I/O ports

• The contents of the control register called the control word

specify an I/O function for each port.

• This register can be accessed to write a control word when A0

& A1 are at logic 1

• Control word register can only be written into and no read

operation of the CW register is allowed.

• Bit D7 of the control register specifies either the I/O function

or the Bit Set/Reset function.

• If Bit D7 =1, bits D6- D1 determine I/O functions in various

mode

• If bit D7 = 0, port C operates in the Bit Set/Reset(BSR)mode.

CONTROL WORD

� BSR mode is concerned only with the eight bits of port C,

which can be set or reset by writing an appropriate control

word in the control register.

� This control word when written in the control register, sets or

resets one bit at a time as specified in the diagram

� In the BSR mode, individual bits of port C can be used for

applications such an on/off switch.

BSR (Bit Set/Reset) Mode

Control Word Format in the BSR Mode

• In this mode, ports A and B are used as two simple 8 bit ports

and port C as two 4 bit ports.

• Each port can be programmed to function as simply an input

port or an output port.

• The input/output features in Mode 0 are

– Outputs are latched

– Input are not latched

– 16 different Input/output configurations possible

Mode 0: Simple Input or Output

Mode 0:Input or Output

� The features of this mode are

◦ Two ports (A and B) function as 8 bit I/O ports. They

can be configured either as input or output ports.

◦ Each port uses three lines from port C as handshake

signals. The remaining two lines of port C can be used

for simple I/O functions.

◦ Input and output data are latched

◦ Interrupt logic is supported.

Mode 1: Input or Output with

handshake

• Ports A and B are configured as input ports

• Port A uses the upper three signals PC3 ,PC4 and PC5 as

handshake signals

• Port B uses the lower three signals PC2, PC1 and PC0 as

handshake signals.

• STB (Strobe Input):This active low signal is generated by

a peripheral device to indicate that it has transmitted a byte

of data. The 8255A in response to STB, generates IBF and

INTR.

Mode 1: Input Control Signals

• IBF(Input Buffer Full):This signal is an acknowledgement by

the 8255A to indicate that the input latch has received the data

byte. This is reset when the MPU reads the data

• INTR(Interrupt Request): This is an output signal that may be

used to interrupt the MPU. This signal is generated if

STB,IBF and INTE(Internal flip-flop) are all at logic 1. This is

reset by the falling edge of the RD signal.

• INTE(Interrupt Enable): This is an internal flip-flop used to

enable or disable the generation of the INTR signal. The two

flip flops INTEA and INTEB are set/reset using the BSR mode.

The INTEA is enabled or disabled through PC4 & INTEB is

enabled or disabled through PC2.

Mode 1 Input Configuration

� OBF (Output buffer full ) – This status signal, whenever falls

to low, indicates that CPU has written data to the specified

output port. The OBF flip-flop will be set by a rising edge of

WR signal and reset by a low going edge at the ACK input.

� ACK ( Acknowledge input ) – ACK signal acts as an

acknowledgement to be given by an output device. ACK

signal, whenever low, informs the CPU that the data

transferred by the CPU to the output device through the port is

received by the output device.

Mode 1: Output Control Signals

• INTR ( Interrupt request ) – Thus an output signal that can

be used to interrupt the CPU when an output device

acknowledges the data received from the CPU. INTR is set

when ACK, OBF and INTE are 1. It is reset by a falling edge

on WR input.

• INTE(Interrupt Enable):The INTEA and INTEB flags are

controlled by the bit set-reset mode of PC6 and PC2respectively.

• PC4,5 :These two lines can be set up either as input or output.

Output Control Signals( cont.)

2/17/2008

• The Salient features of Mode 2 of 8255 are listed as follows:

– The single 8-bit port in group A is available.

– The 8-bit port is bidirectional and additionally a 5-bit control

port is available.

– Three I/O lines are available at port C.( PC2 – PC0 )

– Inputs and outputs are both latched.

– The 5-bit control port C (PC3-PC7) is used for generating /

accepting handshake signals for the 8-bit data transfer on port

A.

Mode 2 Bidirectional Data Transfer

CONTROL WORD FORMATSMode 1 Input Mode 1 Output

Mode 2: Bidirectional Input/Output

Mode 2: Bidirectional Input/Output

• Microprocessor Architecture, Programming and

Applications – Ramesh Gaonkar

• Intel 8255 datasheet www.DatasheetCatalog.com

REFERENCES

2/17/2008

8254 programmable interval timer/counter

• is functionally similar to software designed counters and

timers

• Generates accurate time delays can be used for applications

such as a real time clock, event counter, digital one-shot,

square wave generator & a complex waveform generator

• Includes 3 identical counters that can operate in any one of 6

modes

Introduction

• A 16 bit count is loaded in its register and, on command,

begins to decrement the count until it reaches 0

• At the end of count it generates a pulse that can be used to

interrupt the MPU

• The counter can count either in binary or BCD.

• 8254 is an upgraded version of 8253 and they are pin-

compatible

Introduction(cont.)

• Compatible with All Intel and Most other Microprocessors

• Handles Inputs from DC to 2 MHz

• 8 MHz 8254

• 10 MHz 8254-2

• 8254 includes Status Read-Back Command that can latch the

count and the status of the counters.

• Single 5V Supply

SPECIFICATIONS

• Three counters (0,1 and2)

• Data Bus buffer

• Read/Write control logic

• Control Register

Each counter has two input signals – clock(CLK) and

GATE and one output signal – OUT.

BLOCK DIAGRAM OF 8254


A000 MVI A,80 3E,80 A�80

A002 OUT 43 D3,43 OUTPUT THROUGH CONTROL PORT

A004 MVI A,88 3E,88 A�88

A006 GO OUT 40 D3,40 OUTPUT THROUGH CONTROL PORT

A008 CALL DELAY CD,0F,A0 CALL DELAY PROGRAM

A00B RRC 0F ROTATE RIGHT

A00C JMP GO C3,06,A0 JUMP TO A006

A00F DELAY PUSH B C5 PUSH TO STACK

A010 MVI B,FF 06,FF FF�B

A012 LOOP2 MVI C,06 0E,06 06�C

A014 LOOP1 DCR C 0D C�C-1

A015 JNZ LOOP1 C2,14,A0 JUMP TO A014

A018 DCR B 05 B�B-1

A019 JNZ LOOP2 C2,12,A0 JUMO TO A012

A01C POP B C1 POP STACK

A01D RET C7 RETURN

UNIT-5STEPPER MOTOR CONTROLLER

10.ANALOG TO DIGITAL CONVERTER


8100 START MVI A,90 3E,90 A�90

8102 OUT 43 D3,43 OUT THROUGH A

8104 MVI A,01 BE,01 A�01


8108 MVI A,99 3E,99 A�99

810A OUT 43 D3,43 OUT THROUGH A

810C CHECK IN 42 DB,42 IN THROUGH A

810E ANI 02 E6,02 AND IMMEDIATELY

8110 JNZ CHECK C2,0C,81 JUMP ON NO ZERO

8113 IN 40 DB,40 IN THROUGH A

8115 STA 8206 32,06,82 STORE ACC VALUE


11 DIGITAL TO ANALOG CONVERTER

(a)SQUARE WAVE GENERATOR


8000 START MVI A,80 3E,80 A�80

8002 OUT 43 D3,43 OUT THROUGH 43

8004 L1 MVI A,00 3E,00 A�00


8008 CALL DELAY CD,20,80 CALL DELAY

800B MVI A,FF 3E,FF A�FF

800D OUT 40 DB,40 OUT THROUGH A

800F CALL DELAY CD,20,80 GOTO 8020

8012 JMP L1 C3,04,80 JUMP TO 8004

DELAY PROGRAM

8020 MVI B,6C 06,6C B�6C

8022 L2 DCR B 05 B�B-1

8023 JNZ L2 C2,22,80 IF Z ≠0 GOTO L1

8026 RET C9 RETURN


(b)TRIANGULAR WAVE GENERATOR


8000 START MVI A,80 3E,80 A�80


8004 L3 MVI A,00 3E,00 A�00


8008 L1 INR A 3C INCREMENT A


800B CPI FF FE,FF COMPARE IMM WITH FF

800D JNZ L1 C2,08,80 JUMP IF NO ZERO TO 8008

8010 MVI A,FF 3E,FF A�FF


8014 L2 DCR A 3D DECREMENT A


8017 CPI 40 FE,00 COMPARE IMM WITH 00

8019 JNZ L2 C2,14,80 JUMP TO 8014

801C JMP L3 C3,04,80 JUMP TO 8004


(C)SAWTOOTH GENERATOR


8000 MVI A,80

3E,80 A�80

8002 OUT 43

D3,43 OUT THROUGH A

8004 L2 MVI A,FF

3E,FF A�FF

8006 OUT 40

D3,40 OUT THROUGH A

8008 L1 DCR A

DECREMENT A

8009 OUT 40

D3,40 OUT THROUGH A

800B CPI 00

F3,00 COMPARE IMM WITH 00

800D JNZ L1

C2,08,80 JUMP ON NO ZERO TO 8008

8010 JMP L2

C3,04,80 JUMP TO 8004

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