8051 Microcontroller

Micro-Controller 8051Micro-Controller 8051
OverviewOverview
Ritula Thakur
NITTTR

Chapter 1Chapter 1
The 8051 MicrocontrollersThe 8051 Microcontrollers

OutlinesOutlines
Compare microprocessors & microcontrollers
Advantages of microcontrollers
Embedded systems
Choose a microcontroller
Speed, packaging, memory & cost per unit
Various members of 8051 family
Various manufacturers of 8051
04/07/15 Ritula Thakur 3

Microcontroller vs.Microcontroller vs.
MicroprocessorsMicroprocessors

Embedded Computing SystemsEmbedded Computing Systems
Use a microprocessor or microcontroller to do
one task only
Printer
PC used for any number of applications
Word processor, print-server, bank teller terminal,
video game player, network server, internet
terminal
PC contains or is connected to various
embedded products
Keyboard, printer, modem, disk controller, sound
card, CD-ROM driver, mouse
X86 PC embedded applications04/07/15 Ritula Thakur 5

Embedded Products Using MicrocontrollersEmbedded Products Using Microcontrollers
Home
Appliances, intercom, telephones, security
systems, garage door openers, answering
machines, fax machines, home computers, TVs,
cable TV tuner, VCR, camcorder, remote
controls, video games, cellular phones, musical
instruments, sewing machines, lighting control,
paging, camera, pinball machines, toys,
exercise equipment

Office
Telephones, computers, security systems, fax
machines, microwave, copier, laser printer, color
printer, paging

Auto
Trip computer, engine control, air bag, ABS,
instrumentation, security system, transmission
control, entertainment, climate control, cellular
phone, keyless entry

Choosing A MicrocontrollerChoosing A Microcontroller
Computing needs
Speed, packaging, power consumption, RAM,
ROM, I/O pins, timers, upgrade to high
performance or low-power versions, cost
Software development tools
Assembler, debugger, C compiler, emulator,
technical support
Availability & source

Companies Producing 8051Companies Producing 8051
Table 1-2:Some Companies Producing a
Member of the 8051 Family
CompanyCompany Web SiteWeb Site
IntelIntel www.intel.com/design/mcs51www.intel.com/design/mcs51
AtmelAtmel www.atmel.comwww.atmel.com
Philips/SigneticsPhilips/Signetics www.semiconductors.philips.comwww.semiconductors.philips.com
SiemensSiemens www.sci.siemens.comwww.sci.siemens.com
Dallas SemiconductorDallas Semiconductor www.dalsemi.comwww.dalsemi.com

Inside 8051 MicrocontrollerInside 8051 Microcontroller
Introduced by Intel in 1981

8051 Family8051 Family
Table 1-4:Comparison of 8051 Family
Members
FeatureFeature 80518051 80528052 80318031
ROM (on chip program space in bytes)ROM (on chip program space in bytes) 4K4K 8k8k 0k0k
RAM (bytes)RAM (bytes) 128128 256256 128128
TimersTimers 22 33 22
I/O pinsI/O pins 3232 3232 3232
Serial portSerial port 11 11 11
Interrupt sourcesInterrupt sources 66 88 66

Various 8051 MicrocontrollersVarious 8051 Microcontrollers
8751 microcontroller
UV-EPROM
AT89C51 from Atmel Corporation
Flash (erase before write)
DS5000 from Dallas Semiconductor
NV-RAM (changed one byte at a time), RTC (real-
time clock)
OTP (one-time-programmable) version of
8051
8051 family from Philips
AD, DA, extended I/O, OTP and flash04/07/15 Ritula Thakur 13

Chapter 2Chapter 2
8051 Assembly Language Programming8051 Assembly Language Programming

OutlinesOutlines
8051 registers
Manipulate data using registers & MOVE
instructions
Code simple assembly language instructions
Assemble and run a program
Sequence events upon power-up
Examine programs in ROM codes
ROM memory map
Execution of instructions
Data types
PSW register
RAM memory space
Stack
Register banks

8051 Registers8051 Registers
D7D7 D6D6 D5D5 D4D4 D3D3 D2D2 D1D1 D0D0
DPTR
PC PC (Program counter)
DPH DPL
Figure2-1 (a): Some 8 bit Registers of the 8051
Figure2-1 (b): Some 8051 16 bit Registers
8 bit Registers
R6R6
R5R5
R4R4
R3R3
R2R2
R1R1
R0R0
BB
AA
R7R7

MOV InstructionMOV Instruction
MOV destination, source ; copy source to dest.
MOV A,#55H ;load value 55H into reg. A
MOV R0,A ;copy contents of A into R0
;(now A=R0=55H)
;(now A=R0=R1=55H)
;(now A=R0=R1=R2=55H)
MOV R3,#95H ;load value 95H into R3
;(now R3=95H)
MOV A,R3 ;copy contents of R3 into A
;now A=R3=95H

Notes on ProgrammingNotes on Programming
Value (proceeded with #) can be loaded directly
to registers A, B, or R0 – R7
MOV R5, #0F9H
If values 0 to F moved into an 8-bit register, the
rest assumed all zeros
MOV A, #5
A too large value causes an error
MOV A, #7F2H

ADD InstructionADD Instruction
ADD A, source ;ADD the source operand
;to the accumulator
MOV A, #25H ;load 25H into A
MOV R2,#34H ;load 34H into R2
ADD A,R2 ;add R2 to accumulator
;(A = A + R2)

Structure of Assembly LanguageStructure of Assembly Language
ORG 0H ;start (origin) at location 0
MOV A,#0 ;load 0 into A
ADD A,R5 ;add contents of R5 to A
;now A = A + R5
ADD A,R7 ;add contents of R7 to A
;now A = A + R7
ADD A,#12H ;add to A value 12H
;now A = A + 12H
HERE: SJMP HERE ;stay in this loop
END ;end of asm source file
Program 2-1:Sample of an Assembly Language Program

Steps to Create a ProgramSteps to Create a Program

8051 Program Counter & ROM8051 Program Counter & ROM
SpaceSpace

SpaceSpace

Execute a Program Byte by ByteExecute a Program Byte by Byte
1. PC=0000: opcode 7D fetched; 25 fetched;
R5←25; PC+2
2. PC=0002: opcode 7F fetched; 34 fetched;
R7←34; PC+2
3. PC=0004; opcode 74 fetched; 0 fetched;
A←0; PC+2
4. PC=0006; opcode 2D fetched; A←A+R5;
PC+1
5. (Similarly…)

8051 On-Chip ROM Address Range8051 On-Chip ROM Address Range

Data Types & DirectivesData Types & Directives
ORG 500H
DATA1: DB 28 ;DECIMAL (1C in Hex)
DATA2: DB 00110101B ;BINARY (35 in Hex)
DATA3: DB 39H ;HEX
ORG 510H
DATA4: DB “2591” ; ASCII NUMBERS
ORG 518H
DATA6: DB “My name is Joe” ;ASCII
CHARACTERS

PSW (Flag) RegisterPSW (Flag) Register

Instructions Affecting Flag BitsInstructions Affecting Flag Bits

ADD Instruction and PSWADD Instruction and PSW

8051 RAM Allocation8051 RAM Allocation

8051 Register Banks8051 Register Banks

Access RAM Locations Using Register NamesAccess RAM Locations Using Register Names

Access RAM Locations UsingAccess RAM Locations Using
AddressesAddresses

Switch Register BanksSwitch Register Banks

Pushing onto StackPushing onto Stack

Popping from StackPopping from Stack

Stack & Bank 1 ConflictStack & Bank 1 Conflict

Chapter 3Chapter 3
JUMP, LOOP and CALL InstructionsJUMP, LOOP and CALL Instructions

OutlinesOutlines
Loop instructions
Conditional jump instructions
Conditions determining conditional jump
Unconditional long & short jumps
Calculate target addresses for jumps
Subroutines
Using stack in subroutines
Crystal frequency vs. machine cycle
Code programs to generate time delay

LoopingLooping

Loop inside a Loop (NestedLoop inside a Loop (Nested
Loop)Loop)

8051 Conditional Jump8051 Conditional Jump
InstructionsInstructions

Conditional Jump ExampleConditional Jump Example

Unconditional Jump InstructionsUnconditional Jump Instructions
All conditional jumps are short jumps
Target address within -128 to +127 of PC
LJMP (long jump): 3-byte instruction
2-byte target address: 0000 to FFFFH
Original 8051 has only 4KB on-chip ROM
SJMP (short jump): 2-byte instruction
1-byte relative address: -128 to +127

Calculating Short Jump AddressesCalculating Short Jump Addresses

Call InstructionsCall Instructions
LCALL (long call): 3-byte instruction
2-byte address
Target address within 64K-byte range
ACALL (absolute call): 2-byte instruction
11-bit address
Target address within 2K-byte range

LCALLLCALL

CALL Instruction & Role of StackCALL Instruction & Role of Stack

Using PUSH & POP in SubroutinesUsing PUSH & POP in Subroutines

Calling SubroutinesCalling Subroutines

ACALL (absolute call)ACALL (absolute call)

Programming EfficientlyProgramming Efficiently

Time Delay Generation &Time Delay Generation &
CalculationCalculation
1 instruction = n × machine cycle
1 machine cycle = 12 clock cycles

Delay CalculationDelay Calculation

Delay Calculation ExampleDelay Calculation Example

Increasing Delay Using NOPIncreasing Delay Using NOP

Large Delay Using Nested LoopLarge Delay Using Nested Loop

Chapter 4Chapter 4
I/O Port ProgrammingI/O Port Programming

OutlinesOutlines
8051 pin functions
4 ports of 8051
Dual role of port 0 for data & address
Code assembly language to use ports
Use of port 3 for interrupt signals
Code 8051 instructions for I/O handling
Code bit-manipulation instructions

8051 Pin Diagram8051 Pin Diagram

Clock GenerationClock Generation

Machine & Clock CyclesMachine & Clock Cycles

RESET Value of RegistersRESET Value of Registers

RESET CircuitsRESET Circuits

Pins for External ROM/RAMPins for External ROM/RAM
EA (external access)
VCC: on-chip ROM
GND: external ROM
PSEN (program store enable)
to OE (output enable) pin of ROM
ALE (address latch enable)
to G (enable) pin of 74LS373
See Chapter 14

Port 0: I/O, Open DrainPort 0: I/O, Open Drain
Initially configured as output
MOVMOV A,#55HA,#55H
BACK:BACK: MOVMOV P0,AP0,A
ACALLACALL DELAYDELAY
CPLCPL AA
SJMPSJMP BACKBACK

Port 0: I/O, Open DrainPort 0: I/O, Open Drain

Port 0 as Input: Write all 1sPort 0 as Input: Write all 1s
Dual role of port 0
Can be configured as AD0 – AD7
MOV A,#0FFH ;A = FF hex
MOV P0,A ;make P0 an input port
;by writing all 1s to it
BACK: MOV A,P0 ;get data from P0
MOV P1,A ;send it to port 1
SJMP BACK ;keep doing it

Port 1: I/O, No Pull-up ResistorsPort 1: I/O, No Pull-up Resistors
MOV A,#55H
BACK: MOV P1,A
ACALL DELAY
CPL A
SJMP BACK
MOV A,#0FFH ;A=FF hex
MOV P1,A ;make P1 an input port
;by writing all 1s to it
MOV A,P1 ;get data from P1
MOV R7,A ;save it in reg R7
ACALL DELAY ;wait
MOV A,P1 ;get another data from
P1
ACALL DELAY ;wait
MOV A,P1 ;get another data from P1

MOV A,#55H
BACK: MOV P2,A
ACALL DELAY
CPL A
SJMP BACK
MOV A,#0FFH ;A=FF hex
MOV P2,A ;make P2 an input port by
;writing all 1s to it
BACK: MOV A,P2 ;get data from P2
MOV P1,A ;send it to Port 1
SJMP BACK ;keep doing that
♦ Dual role of port 2: A8-A15Dual role of port 2: A8-A15

Different Ways of Accessing 8 bitsDifferent Ways of Accessing 8 bits
BACK: MOV A,#55H
MOV P1,A
ACALL DELAY
MOV A,#0AAH
MOV P1,A
ACALL DELAY
SJMP BACK
BACK:BACK: MOVMOV P1,#55HP1,#55H
MOVMOV P1,#0AAHP1,#0AAH
SJMPSJMP BACKBACK
MOV P1,#55H ;P1=01010101
AGAIN: XLR P1,#0FFH ;EX-OR
;P1 with 1111 1111
ACALL DELAY
SJMP AGAIN

Single-bit Addressability of PortsSingle-bit Addressability of Ports
BACK: CPL P1.2 ;complement P1.2 only
ACALL DELAY
SJMP BACK
;another variation of the above program follows
AGAIN: SETB P1.2 ;change only P1.2=high
ACALL DELAY
CLR P1.2 ;change only P1.2=low
ACALL DELAY
SJMP AGAIN

Single-bit Addressability of PortsSingle-bit Addressability of Ports

Example 4-2Example 4-2

Chapter 5Chapter 5
Addressing ModesAddressing Modes

OutlinesOutlines
Five addressing modes of 8051
Code instructions using each addressing
mode
Access RAM using various addressing
modes
SFR addresses
Access SFR
Operate stack using direct addressing mode
Code instructions to operate look-up table

Five Addressing ModesFive Addressing Modes
Immediate
Register
Direct
Register indirect
Indexed

Immediate Addressing ModeImmediate Addressing Mode
MOVMOV A,#25HA,#25H ;load 25H into A;load 25H into A
MOVMOV R4,#62R4,#62 ;load the decimal value 62 into R4;load the decimal value 62 into R4
MOV B,#40HMOV B,#40H ;load 40H into B;load 40H into B
MOVMOV DPTR,#4521HDPTR,#4521H ;DPTR=4521H;DPTR=4521H
MOVMOV DPTR,#2550HDPTR,#2550H
;is the same as:;is the same as:
MOVMOV DPL,#50HDPL,#50H
MOVMOV DPH,#25HDPH,#25H

MOVMOV DPTR,#68975DPTR,#68975 ;illegal!! value > 65535 (FFFFH);illegal!! value > 65535 (FFFFH)
COUNTCOUNT EQU 30EQU 30
…… ……
MOVMOV R4,#COUNTR4,#COUNT ;R4=1E (30=1EH);R4=1E (30=1EH)
MOVMOV DPTR,#MYDATADPTR,#MYDATA ;DPTR=200H;DPTR=200H
ORGORG 200H200H
MYDATA:MYDATA: DB “America”DB “America”

Register Addressing ModeRegister Addressing Mode
MOVMOV A,R0A,R0 ;copy the contents of R0 into A;copy the contents of R0 into A
MOVMOV R2,AR2,A ;copy the contents of A into R2;copy the contents of A into R2
ADDADD A,R5A,R5 ;add the contents of R5 to contents of A;add the contents of R5 to contents of A
ADDADD A,R7A,R7 ;add the contents of R7 to contents of A;add the contents of R7 to contents of A
MOVMOV R6,AR6,A ;save accumulator in R6;save accumulator in R6
MOVMOV DPTR,#25F5HDPTR,#25F5H
MOVMOV R7,DPLR7,DPL
MOVMOV R6,DPHR6,DPH

Direct Addressing ModeDirect Addressing Mode
RAM addresses 00 to 7FH
MOVMOV R0,40HR0,40H ;save content of RAM location 40H in R0;save content of RAM location 40H in R0
MOVMOV 56H,A56H,A ;save content of A in RAM location 56H;save content of A in RAM location 56H
MOVMOV R4,7FHR4,7FH ;move contents of RAM location 7FH to;move contents of RAM location 7FH to
R4R4
MOVMOV A,4A,4 ;is same as;is same as
MOV A,R4MOV A,R4 ;which means copy R4 into A;which means copy R4 into A
MOVMOV A,7A,7 ;is same as;is same as
MOVMOV A,R7A,R7 ;which means copy R7 into A;which means copy R7 into A

MOVMOV A,2A,2 ;is the same as;is the same as
MOVMOV A,0A,0 ;is the same as;is the same as
MOVMOV R2,#5R2,#5 ;R2=05;R2=05
MOVMOV A,2A,2 ;copy R2 to A (A=R2=05);copy R2 to A (A=R2=05)
MOVMOV B,2B,2 ;copy R2 to B (B=R2=05);copy R2 to B (B=R2=05)
MOVMOV 7,27,2 ;copy R2 to R7;copy R2 to R7
;since “MOV R7,R2” is invalid;since “MOV R7,R2” is invalid

SFR Registers & Their AddressesSFR Registers & Their Addresses
MOVMOV 0E0H,#55H0E0H,#55H ;is the same as;is the same as
MOVMOV A,#55HA,#55H ;which means load 55H into A (A=55H);which means load 55H into A (A=55H)
MOVMOV 0F0H,#25H0F0H,#25H ;is the same as;is the same as
MOV B,#25HMOV B,#25H ;which means load 25H into B (B=25H);which means load 25H into B (B=25H)
MOVMOV 0E0H,R20E0H,R2 ;is the same as;is the same as
MOVMOV 0F0H,R00F0H,R0 ;is the same as;is the same as
MOVMOV B,R0B,R0 ;which means copy R0 into B;which means copy R0 into B

SFR Addresses ( 1 of 2 )SFR Addresses ( 1 of 2 )

SFR Addresses ( 2 of 2 )SFR Addresses ( 2 of 2 )

ExampleExample

Stack and Direct Addressing ModeStack and Direct Addressing Mode
Only direct addressing is allowed for stack

Register Indirect Addressing ModeRegister Indirect Addressing Mode
Only R0 & R1 can be used
MOVMOV A,@R0A,@R0 ;move contents of RAM location whose;move contents of RAM location whose
;address is held by R0 into A;address is held by R0 into A
MOVMOV @R1,B@R1,B ;move contents of B into RAM location;move contents of B into RAM location
;whose address is held by R1;whose address is held by R1

Example ( 1 of 2 )Example ( 1 of 2 )

Advantage of Register Indirect AddressingAdvantage of Register Indirect Addressing
Looping not possible in direct addressing

ExampleExample

Index Addressing Mode & On-chip ROMIndex Addressing Mode & On-chip ROM
AccessAccess
Limitation of register indirect addressing: 8-bit
addresses (internal RAM)
DPTR: 16 bits
MOVC A, @A+DPTR ; “C” means program
(code) space ROM

Look-up Table & IndexedLook-up Table & Indexed
AddressingAddressing

ExampleExample

Chapter 6Chapter 6
Arithmetic Instructions and ProgramsArithmetic Instructions and Programs

OutlinesOutlines
Range of numbers in 8051 unsigned data
Addition & subtraction instructions for unsigned
data
BCD system of data representation
Packed and unpacked BCD data
Addition & subtraction on BCD data
Range of numbers in 8051 signed data
Signed data arithmetic instructions
Carry & overflow problems & corrections

Addition of Unsigned NumbersAddition of Unsigned Numbers
ADD A, source ; A = A + source

Addition of Individual BytesAddition of Individual Bytes

ADDC & Addition of 16-bitADDC & Addition of 16-bit
NumbersNumbers
1
3C E7
3B 8D
78 74
+

BCD Number SystemBCD Number System
Unpacked BCD: 1 byte
Packed BCD: 4 bits

Adding BCD Numbers & DAAdding BCD Numbers & DA
InstructionInstruction
MOVMOV A,#17HA,#17H
ADDADD A,#28HA,#28H
MOVMOV A,#47HA,#47H ;A=47H first BCD operand;A=47H first BCD operand
MOVMOV B,#25HB,#25H ;B=25 second BCD operand;B=25 second BCD operand
ADDADD A,BA,B ;hex (binary) addition (A=6CH);hex (binary) addition (A=6CH)
DADA AA ;adjust for BCD addition;adjust for BCD addition
(A=72H)(A=72H)
HEXHEX BCDBCD
2929 0010 10010010 1001
++ 1818 ++0001 10000001 1000
4141 0100 00010100 0001 AC=1AC=1
++ 66 ++ 01100110
4747 0100 01110100 0111

ExampleExample

Subtraction of Unsigned NumbersSubtraction of Unsigned Numbers
SUBB A, source ; A = A – source – CY
SUBB when CY = 0
Take 2’s complement of subtraend (source)
Add it to minuend
Invert carry

Example (Positive Result)Example (Positive Result)

Example (Negative Result)Example (Negative Result)

SUBB When CY = 1SUBB When CY = 1
For multibyte numbers

Multiplication of UnsignedMultiplication of Unsigned
NumbersNumbers
MUL AB ; A × B, place 16-bit result in B and
AMOVMOV A,#25HA,#25H ;load 25H to reg. A;load 25H to reg. A
MOVMOV B,#65HB,#65H ;load 65H in reg. B;load 65H in reg. B
MULMUL ABAB ;25H * 65H = E99 where;25H * 65H = E99 where
;B = 0EH and A = 99H;B = 0EH and A = 99H
Table 6-1:Unsigned Multiplication Summary (MUL AB)Table 6-1:Unsigned Multiplication Summary (MUL AB)
MultiplicationMultiplication Operand 1Operand 1 Operand 2Operand 2 ResultResult
bytebyte ×× bytebyte AA BB A=low byte,A=low byte,
B=high byteB=high byte

Division of Unsigned NumbersDivision of Unsigned Numbers
DIV AB ; divide A by B
MOVMOV A,#95HA,#95H ;load 95 into A;load 95 into A
MOVMOV B,#10HB,#10H ;load 10 into B;load 10 into B
DIVDIV ABAB ;now A = 09 (quotient) and;now A = 09 (quotient) and
;B = 05 (remainder);B = 05 (remainder)
Table 6-2:Unsigned Division Summary (DIV AB)Table 6-2:Unsigned Division Summary (DIV AB)
DivisionDivision NumeratorNumerator DenominatorDenominator QuotientQuotient RemainderRemainder
byte / bytebyte / byte AA BB AA BB

Signed 8-bit OperandsSigned 8-bit Operands
Covert to 2’s complement
Write magnitude of number in 8-bit binary (no
sign)
Invert each bit
Add 1 to it

ExampleExample

Byte-sized Signed Numbers RangesByte-sized Signed Numbers Ranges
DecimalDecimal BinaryBinary HexHex
-128-128 1000 00001000 0000 8080
-127-127 1000 00011000 0001 8181
-126-126 1000 00101000 0010 8282
…….. …………………… ....
-2-2 1111 11101111 1110 FEFE
-1-1 1111 11111111 1111 FFFF
00 0000 00000000 0000 0000
+1+1 0000 00010000 0001 0101
+2+2 0000 00100000 0010 0202
…… …………………… ......
+127+127 0111 11110111 1111 7F7F

Overflow in Signed NumberOverflow in Signed Number
OperationsOperations

When Is the OV Flag Set?When Is the OV Flag Set?
Either: there is a carry from D6 to D7 but no
carry out of D7 (CY = 0)
Or: there is a carry from D7 out (CY = 1) but no
carry from D6 to D7

ExampleExample

Chapter 7Chapter 7
LOGIC INSTRUCTIONS ANDLOGIC INSTRUCTIONS AND
PROGRAMSPROGRAMS

OutlinesOutlines
Define the truth tables for logic functions AND, OR,
XOR
Code 8051 Assembly language logic function
instructions
Use 8051 logic instructions for bit manipulation
Use compare and jump instructions for program
control
Code 8051 rotate and swap instructions
Code 8051 programs for ASCII and BCD data
conversion

ANDAND
XX YY X AND YX AND Y
00 00 00
00 11 00
11 00 00
11 11 11
ANL destination, source ;dest = dest AND
source

OROR
ORL destination, source ;dest = dest ORORL destination, source ;dest = dest OR
sourcesourceXX YY X AND YX AND Y
00 00 00
00 11 11
11 00 11
11 11 11

XORXOR
XRL destination, source ;dest = dest XORXRL destination, source ;dest = dest XOR
sourcesourceXX YY X AND YX AND Y
00 00 00
00 11 11
11 00 11
11 11 00
XRL A,#04H ;EX-OR A with 0000 010004/07/15 Ritula Thakur 147

XORXOR

CPL (complement accumulator)CPL (complement accumulator)
MOVMOV A,#55HA,#55H
CPLCPL AA ;now A=AAH;now A=AAH
;0101 0101(55H) becomes;0101 0101(55H) becomes
;1010 1010 (AAH);1010 1010 (AAH)

Compare instructionCompare instruction
CJNE destination, source ,relative addressCJNE destination, source ,relative address

Table 7-1:Carry Flag Setting For CJNE InstructionTable 7-1:Carry Flag Setting For CJNE Instruction
CompareCompare Carry FlagCarry Flag
destination > sourcedestination > source CY = 0CY = 0
destination < sourcedestination < source CY = 1CY = 1
CJNE R5,#80,NOT_EQUAL ;check R5 for 80
…. ;R5=80
NOT_EQUAL: JNC NEXT ;jump if R5>80
…. ;R5<80
NEXT: ….

Rotating the bits of A right and leftRotating the bits of A right and left
RRRR AA ;rotate right A;rotate right A
MOV A,#36H ;A=0011 0110
RR A ;A=0001 1011
RR A ;A=1000 1101
RR A ;A=1100 0110
RR A ;A=0110 0011
RL A ;rotate left A

MOV A,#72H ;A=0111 0010
RL A ;A=1110 0100
RL A ;A=1100 1001

Rotating through the carryRotating through the carry
RRCRRC AA ;rotate right through carry;rotate right through carry
CLR C ;make CY=0
MOV A,#26H ;A=0010 0110
RRC A ;A=0001 0011 CY=0
RRC A ;A=0000 1001 CY=1
RRC A ;A=1000 0100 CY=1
RLC A ;rotate left through carry

SETB C ;make CY=1
MOV A,#15H ;A=0001 0101
RLC A ;A=0010 1010 CY=0
RLC A ;A=0101 0110 CY=0
RLC A ;A=1010 1100 CY=0
RLC A ;A=0101 1000 CY=1

SWAPSWAP AA

RRC A ;first bit to carry
MOV P1.3,C ;output carry as data bit
RRC A ;second bit to carry
RRC A ;third bit to carry
…..

BCD AND ASCII APPLICATIONBCD AND ASCII APPLICATION
PROGRAMPROGRAM

Packed BCD to ASCII conversionPacked BCD to ASCII conversion
Packed BCDPacked BCD Unpacked BCDUnpacked BCD ASCIIASCII
29H29H 02H & 09H02H & 09H 32H & 39H32H & 39H
0010 10010010 1001 0000 0010 &0000 0010 & 0011 0010 &0011 0010 &
0000 10010000 1001 0011 10010011 1001

ASCII to packed BCD conversionASCII to packed BCD conversion
Key ASCII Unpacked BCDKey ASCII Unpacked BCD Packed BCDPacked BCD
44 34 0000010034 00000100
77 37 00000111 01000111 or 47H37 00000111 01000111 or 47H
MOV A,#’4’ ;A=34H, hex for ASCII char 4
MOV R1,#’7’ ;R1=37H, hex for ASCII char 7
ANL A,#0FH ;mask upper nibble (A=04)
ANL R1,#0FH ;mask upper nibble (R1=07)
SWAP A ;A=40H
ORL A,R1 ;A=47H, packed BCD

Chapter 8Chapter 8
SINGLE-BIT INSTRUCTIONSSINGLE-BIT INSTRUCTIONS
AND PROGRAMMINGAND PROGRAMMING

OutlinesOutlines
List the 8051 Assembly language instructions for bit
manipulation
Code 8051 instructions for bit manipulation of ports
Explain which 8051 registers are bit-addressable
Describe which portions of the 8051 RAM are bit-
addressable
Discuss bit manipulation of the carry flag
Describe the carry flag bit-related instructions of the
8051

Single-bit instructionsSingle-bit instructions

I/O ports and bit-addressabilityI/O ports and bit-addressability
The 8051 has four I/O ports, each of which is 8 bits

Checking an input bitChecking an input bit
JNB (jump if no bit) ; JB (jump if bit = 1)

Registers and bit-addressabilityRegisters and bit-addressability

Figure 8-2. Bits of the PSW Register

Bit-addressable RAMBit-addressable RAM

Single-bit operations with CYSingle-bit operations with CY

Instructions for reading input portInstructions for reading input port
READING INPUT PINS VS. PORT LATCHREADING INPUT PINS VS. PORT LATCH
In Reading a port:
1.Read the status of the input pin
2.Read the internal latch of the output port

Reading latch for output portReading latch for output port

8051 Timers8051 Timers
Basic Registers of the timer
Timer 0 registers
Timer 1 registers
Both the registers are 16 bits wide but can be
accessed as 8 bit registers separately.

PROGRAMMING 8051 TIMERSPROGRAMMING 8051 TIMERS
Timer 0 registersTimer 0 registers
TL0 ( timer 0 low byte )
TH0 ( timer 0 high byte )

Timer 1 registersTimer 1 registers
TL1 ( timer 1 low byte )
TH1 ( timer 1 high byte )

04/07/15 Ritula Thakur
Timer Interrupt & OptimizeTimer Interrupt & Optimize
TMOD Register - Operation ControlTMOD Register - Operation Control
TIMER1 TIMER2
M1 M1M0GATE C/T GATE C/T M0
(MSB) (LSB)
GATE Gating Control
When Set Timer/Counter “x”is enabled
Only while “INTx”pin is high and “TRx” control pin is set
When Cleared Timer “x” is enabled
Whenever “TRx” control bit is set
C/T Timer or Counter Selector
Cleared for Timer operation (input from internal system clock).
Set for Counter operation (input from “Tx” input pin)
193

Chap3. Timer Interrupt & OptimizeChap3. Timer Interrupt & Optimize
TMOD Register - Operating Mode Control (0 , 1, 2 )TMOD Register - Operating Mode Control (0 , 1, 2 )
TIMER1 TIMER2
GATE C/T GATE C/TM1 M1M0 M0
(MSB) (LSB)
8048 TIMER : ”TLx” serves as 5-bit prescaler.
16-bit Timer/Counter : “THx” and “TLx” are
cascaded
8-bit auto reload
“THx” hold a value which is to be
Reloaded into “TLx” each time it overflows
M1 M0 Function
0 0
0 1
1 0
194

Indicate which mode and which timer are
selected for each of the following:
MOV TMOD,#01H
MOV TMOD,#20H
TMOD=00000001, mode 1 of Timer 0
TMOD=00100000, mode 2 of Timer 1

Clock Source for timerClock Source for timer
The crystal frequency attached to the 8051
timer is the source of the clock for the timer.
The frequency for the timer is always 1/12th
the
frequency of the crystal attached to the 8051

Mode 1 programmingMode 1 programming
1. It is a 16-bit timer; so it allows values of 0000 to FFFFH
to be loaded into the timer’s registers TL and TH
After TH and TL are loaded with a 16 bit initial value, the
timer must be started (SETB TR0 and SETB TR1)
It starts counting up until it reaches its limit of FFFFH.
When it rolls over from FFFFH to 0000, it sets high TF
(Timer flag)
Stop the timer (CLR TR0 & CLR TR1)
After the timer reaches its limit and rolls over, in order to
repeat the process TH and TL must be reloaded with the
original value, and TF must be reset to 0

Mode 1 programmingMode 1 programming
1.Loaded value into TL and TH
2.”SETB TR0” for timer 0 ;”SETB TR1” for timer 1
3.If TF (timer flag) = high “CLR TR0” or “CLR TR1”
4.Reloaded TH and TL value, TF reset to 0

Steps to program in mode 1Steps to program in mode 1
1.Load the TMOD value
2.Load registers TL and TH
3.Start the timer (SETB TR0 or SETB TR1)
4.Keep monitoring the timer flag (TF)
5.Stop the timer (CLR TR0 or CLR TR1)
6.Clear the TF flag
7.Go back to step 2

Calculate Timer DelayCalculate Timer Delay

Finding values to be loaded into the timerFinding values to be loaded into the timer
Assuming XTAL =11.0592MHz from Example 9-10
1.Divide the desired time delay by 1.085μs
2.Perform 65536-n, where n is the decimal value we got in
Step 1
3.Convert the result of Step 2 to hex, where yyxx is the
initial hex value to be loaded into the timer’s registers
4.Set TL = xx and TH = yy

Chap3. Timer Interrupt & OptimizeChap3. Timer Interrupt & Optimize
osc 12÷
1/ =TC CONTROL
TL1
(8BITS)
TH1
(8BITS)
TF1 INTERRUPT
GATE
PININT1
TR1
T1 PIN
0/ =TC
Timer/Counter 1 Mode 1:16-bit Counter
Timer Mode - Mode 1
207

Mode 0Mode 0
Like mode 1 except that it is a 13-bit timer
Mode 2 ProgrammingMode 2 Programming
1.Loaded value into TH (8-bit timer)
2.”SETB TR0” for timer 0 ;”SETB TR1” for timer 1
3.If TF (timer flag) = high “CLR TR0” or “CLR TR1”
4.Reloaded TL value kept by TH

Steps to program in mode 2Steps to program in mode 2
1.Load the TMOD value
2.Load the TH registers
3.Start the timer
4.Keep monitoring the timer flag (TF)
5.Clear the TF flag
7.Go back to step 4

8051 SERIAL COMMUNICATION8051 SERIAL COMMUNICATION

OutlinesOutlines
Contrast and compare serial versus parallel
communication
List the advantages of serial communication
over parallel
Explain serial communication protocol
Contrast synchronous versus asynchronous
communication
Contrast half-versus full-duplex transmission

♦ Explain the process of data framingExplain the process of data framing
♦ Describe data transfer rate and bps rateDescribe data transfer rate and bps rate
♦ Define the RS232 standardDefine the RS232 standard
♦ Explain the use of the MAX232 andExplain the use of the MAX232 and
MAX233 chipsMAX233 chips
♦ Interface the 8051 with an RS232Interface the 8051 with an RS232
connectorconnector
♦ Discuss the baud rate of the 8051Discuss the baud rate of the 8051
♦ Describe serial communication features ofDescribe serial communication features of
the 8051the 8051
♦ Program the 8051 for serial dataProgram the 8051 for serial data

Basics of serial communicationBasics of serial communication

Start and stop bitsStart and stop bits

RS232 pinsRS232 pins

Data communication classificationData communication classification

RxD and TxD pins in the 8051RxD and TxD pins in the 8051
TxD pin 11 of the 8051 (P3.1)
RxD pin 10 of the 8051 (P3.0)

MAX232MAX232

MAX233MAX233

8051 SERIAL COMMUNICATION8051 SERIAL COMMUNICATION
PROGRAMMINGPROGRAMMING

Baud Rate in 8051Baud Rate in 8051
The baud rate in 8051 is programmable (done
with the help of timer 1)
Relation b/w crystal frequency and baud rate
8051 divides crystal frequency by 12 to get m/c
cycle frequency
8051’s serial commn UART crctry divides it by
32 once more
11.0592/12=921.6 kHz
921.6 kHz/32=28,800 Hz

SBUF registerSBUF register
MOV SBUF,#’D’ ;load SBUF=44H, ASCII for ‘D’
MOV SBUF,A ;copy accumulator into SBUF
MOV A,SBUF ;copy SBUF into accumulator

SCON (Serial control) registerSCON (Serial control) register

SM0,SM1SM0,SM1
SM0 and SM1 are D7 and D6 of the SCON
SM0 SM1
0 0 Serial Mode 0
0 1 Serial Mode 1,8 bit data,
1 stop bit, 1 start bit
1 0 Serial Mode 2
1 1 Serial Mode 3

Programming the 8051 to transfer dataProgramming the 8051 to transfer data
seriallyserially
TMOD register is loaded with 20H to set the baud rate)
TH1 is loaded to set the baud rate for serial data transfer
SCON is loaded with 50H
TR1 is set to start the Timer 1
Character byte to be transferred is written into SBUF
register
TI flag is monitored to see if the character has been
transferred completely
TI is cleared by CLR TI
To transfer the next character, go to Step 6

Programming the 8051 to transferProgramming the 8051 to transfer
data seriallydata serially

Programming the 8051 to receive dataProgramming the 8051 to receive data
seriallyserially
TMOD register is loaded with 20H to set the baud rate)
TH1 is loaded to set the baud rate for serial data transfer
SCON is loaded with 50H
TR1 is set to start the Timer 1
Character byte to be transferred is written into SBUF
register
RI flag is monitored to see if the character has been
transferred completely
RI is cleared by CLR TI
To receive the next character, go to Step 6

Programming the 8051 to receiveProgramming the 8051 to receive
data seriallydata serially

Doubling the baud rate in theDoubling the baud rate in the
80518051
1. To use a higher frequency crystal
2. To change a bit in the PCON register
SMODSMOD ---- ---- ---- GF1GF1 GF0GF0 PDPD IDLIDL
D7 D0
MOV A,PCON ;place a copy of PCON in ACC
SETB ACC.7 ;make D7=1
MOV PCON,A ;now SMOD=1 without
;changing any other bits

Baud rates for SMOD=0Baud rates for SMOD=0
Machine cycle freq. = 11.0592 MHz / 12 = 921.6 kHz
and
921.6 kHz / 32 = 28,800 Hz since SMOD = 0

Baud rates for SMOD=1Baud rates for SMOD=1
Machine cycle freq. = 11.0592 MHz / 12 = 921.6 kHz
and
921.6 kHz / 16 = 57,600 Hz since SMOD = 1

Chapter 11Chapter 11
INTERRUPTS PROGRAMMINGINTERRUPTS PROGRAMMING

OutlinesOutlines
Contrast and compare interrupts versus polling
Explain the purpose of the ISR
List the 6 interrupts of the 8051
Explain the purpose of the interrupt vector
table
Enable or disable 8051 interrupts
Program the 8051 timers using interrupts
Describe the two external hardware interrupts
of the 8051

♦ Contrast edge-triggered with level-triggeredContrast edge-triggered with level-triggered
interruptsinterrupts
♦ Program the 8051 for interrupt-based serialProgram the 8051 for interrupt-based serial
communicationcommunication
♦ Define the interrupt priority of the 8051Define the interrupt priority of the 8051

Six interrupts in the 8051Six interrupts in the 8051

Step in enabling an interruptStep in enabling an interrupt

PROGRAMMING TIMERPROGRAMMING TIMER
INTERRUPTSINTERRUPTS

Roll-over timer flag andRoll-over timer flag and
interruptinterrupt
JNB TF, target

Programming externalProgramming external
hardware interruptshardware interrupts

Sampling the low level-Sampling the low level-
triggered interrupttriggered interrupt

Edge-triggered interruptsEdge-triggered interrupts

Sampling the edge-triggeredSampling the edge-triggered
interruptinterrupt

RI and TI flags and interruptsRI and TI flags and interrupts

Use of serial COM in the 8051Use of serial COM in the 8051

Clearing RI and TI before theClearing RI and TI before the
RETI instructionRETI instruction
CLR TI ; CLR RI

Interrupt priority upon resetInterrupt priority upon reset

Setting interrupt priority with the IPSetting interrupt priority with the IP
registerregister

8051 Microcontroller

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