Microcontrollers

8051

CPU

General-Purpose Micro-processor

RAM ROM I/O Port

TimerSerial COM Port

Data Bus

Address Bus

General-Purpose Microprocessor System

Microprocessors:

• CPU for Computers

• No RAM, ROM, I/O on CPU chip itself

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

Many chips on mother’s board

General-purpose microprocessor

RAM ROM

I/O Port

TimerSerial COM Port

Microcontroller

CPU

• A smaller computer

• On-chip RAM, ROM, I/O ports...

• Example ： 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

Advantages over mp

• Cost is lower• Standalone mp never used – memory, I/O,

clock necessary• For mp- large size PCB • Large PCB- more effort and cost• Big physical size• More difficult to trouble shoot mp based• A mc is a mp with integrated peripherals.

Advantages of mc

• Low cost• Small size of product• Easy to troubleshoot and maintain• More reliable• Additional mem, I/o can also be added• Software security feature• All features available with 40 pins. • Useful for small dedicated applications and not for larger

system designs which may require many more I/O ports. • Mostly used to implement small control functions.

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

Pin Description of the 8051Pin Description of the 8051

1234567891011121314151617181920

4039383736353433323130292827262524232221

P1.0P1.1P1.2P1.3P1.4P1.5P1.6P1.7RST

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

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

XTAL2XTAL1

GND

(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/PROGPSENP2.7(A15)P2.6(A14)P2.5(A13)P2.4(A12)P2.3(A11)P2.2(A10)P2.1(A9)P2.0(A8)

8051(8031)

Register Set of 8051-SFR• Special Function Registers (SFR) are

special purpose registers – 21 in number• Addresses from 80H to FFH of all SFR’s• Two 8 bit regist. A and B – store operands• A, B, PSW, P0-P3, IP, IE, TCON,SCON

– Bit addressable, 8bit each, 11 in number• SP, DPH,DPL,TMOD,TH0,TL0,TH1,TL1,SBUF,PCON

– Byte addressable, 8bit each. – DPTR – data pointer, accesses ext. mem. DPH + DPL = DPTR

• Starting 32 bytes of RAM – general purpose reg, divided into 4 register banks of 8 registers each. Only one of these bank accessible at one time. RS1 and RS0 of PSW used to select bank.

Register Set of 8051-SFR• TH0-TL0 and TH1-TL1

– 16 bit timer registers

• P0-P3 – port latches• SP, PSW, IP – Interrupt Priority, IE – enable• TCON – timer/counter control reg to turn on/off the

timers, interrupt control flags for ext. int like INT1 and INT0

• TMOD – modes of operation of timer/counter• SCON – serial port mode control reg• SBUF – serial data buffer for transmit and receive• PCON – Power control reg – power down bit, idle bit

RegistersA

B

R0

R1

R3

R4

R2

R5

R7

R6

DPH DPL

PC

DPTR

PC

Some 8051 16-bit Register hold addresses

Some 8-bitt Registers of the 8051

PSW (8)

SP (8)

8051 features• Internal ROM – 4K, RAM – 128bytes

• Thirty two I/O pins as 4 – 8 bit ports P0 –P3

• Two 16 bit timer/counters T0 and T1• Full duplex serial data receiver/trans. SBUF

• Control registers – TCON, TMOD, SCON, PCON, IP and IE

• Two external and three Internal Interrupt sources

• Oscillator and clock circuits

PCON

• Idle mode – oscillator, serial port, interrupt, timer blocks are active but clock disabled.

• Can be terminated with INT or reset

• Power down mode – on-chip osc stopped. RAM contents preserved. Hardware reset

• Two general purpose flags and a double baud bit.

TMOD Register:

• Gate : When set, timer only runs while INT(0,1) is high.

• C/T : Counter/Timer select bit.

• M1 : Mode bit 1.• M0 : Mode bit 0.

TCON Register:

• TF1: Timer 1 overflow flag.• TR1: Timer 1 run control bit.• TF0: Timer 0 overflag.• TR0: Timer 0 run control bit.• IE1: External interrupt 1 edge flag.• IT1: External interrupt 1 type flag.• IE0: External interrupt 0 edge flag.• IT0: External interrupt 0 type flag.

Memory addressing• Program memory - EPROM

– Intermediate results, variables, const– 4KB internal from 0000 – 0FFFH– 64KB external with PSEN, till FFFFH– Internal –external difference PSEN

• Data Memory – RAM– 64KB of external with DPTR signal– Internal memory two parts - 128 bytes Internal RAM

and secondly set of addresses from 80-FFH for SFR’s

– 128 bytes from 00 – 7FH direct or indirect– SFR addresses – only direct addressing mode

Memory Addressing

• Lower 128 bytes in three sections– 00-1F – 32 bytes 4 banks 00,01,10,11 each

containing 8 registers of 8 bits each. Only one accessible at a time with PSW bits.

– 20-2FH – 16bytes is bit addressable with addresses 0F to 7FH, 20.7 or 20.0, or 0-7

– 30-7F – 80 bytes of general purpose data memory. It is byte addressable, used for stack

• RAM memory space allocation in the 8051

7FH

30H

2FH

20H

1FH

17H

10H

0FH

07H

08H

18H

00HRegister Bank 0

(Stack )Register Bank 1

Register Bank 2

Register Bank 3

Bit-Addressable RAM

Scratch pad RAM

External I/O interfacing

• 8051 has two timers, one Serial i/o port and 4 – 8bit addressable ports.

• More I/O as external memory-mapped I/O

Interrupts of 8051

• 5 sources of Interrupts– INT0 and INT1 bars external interrupt inputs

• These are processed internally by IE0 and IE1 flags

– Two timers which generate int when FFFFH– Serial port interrupt if R1 or T1 is set.

• Single step int by software

Interrupt Enable Register :

• EA : Global enable/disable.• --- : Undefined.

• ET2 :Enable Timer 2 interrupt.• ES :Enable Serial port interrupt.• ET1 :Enable Timer 1 interrupt.• EX1 :Enable External 1 interrupt.• ET0 : Enable Timer 0 interrupt. • EX0 : Enable External 0 interrupt.

Addressing modes• Direct - MOV R0, 89 H, Eg 89 of TMOD

– operands 8 bit address field– Internal data RAM and SFRS only

• Indirect - ADD A, @ R0

– Address is stored in R0 or R1 or SP if 8bits

– 16 bit addresses only in DPTR

• Register Instructions - ADD A, R7

– Operands in R0 – R7 of selected register bank. Register bank selected by two bank select bits of PSW

• Register specific (Register Implicit) RLA• Immediate Mode ADD A, #100• Indexed Addressing

Addressing Modes

• Indexed Addressing– MOVC A, @A+DPTR– JMP @ A + DPTR– Used to access only program memory not data– Used for look up table manipulations– Only PC or data pointer – 16 bit storage registers allowed– Base address in PC or DPTR, relative addr in A

Identify the addressing modes

• MOV A,#50H• MOV A, R5• MOV DPTR,#nn• MOV 90H, #0a5H• MOV 0A8H, 77H• MOV @R1,#n• MOV A, @R0• MOVX @DPTR,A• MOVC A, @A+PC

• Explain the internal and external program memory as well as data memory of 8051 with the diagram showing their capacities.

• Draw the diagram to Interface Program memory of 16K x 8 EPROM to 8051and give its memory map. The address of memory map should start from 0000H.

• Discuss about various addressing modes of 8051.• Explain the interrupt structure. Mention the priority. Explain how least priority

is made as highest priority? • Explain in 8051 instruction set to handle bit addressable RAM. • Draw and discuss the formats and bit definitions of the following SFR’s .(a)

IP(b) TMOD(c) TCON(d) SCON • (a) Explain the internal RAM organization of 8051? Discuss how switching

between register banks is possible? • What is the use of SFR? List out the SFR of 8051? • Discuss the advantages of microcontroller based systems over

microprocessor based systems?• (b) With a neat sketch discuss the internal architecture of 8051?

Explain the Flags d program status word of 8051 microcontroller? • Explain the different types of Interrupt in 8051.• Discuss the register set of 8051• Explain the addressing modes of 8051 microcontroller. • Explain the different modes of operation of timer/counter in 8051.• How does 8051 differentiate between the external and Internal prog mem