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26 February 2014 M.M.Arun Prasath., AP/ECE
UNIT – IV 8 BIT MICROCONTROLLER – H/W
ARCHITECTURE, INSTRUCTION SET AND PROGRAMMING
RAM ROM
I/O
Port Timer
Serial
COM
Port
Microcontroller
CPU
INTRODUCTION
A smaller computer
On-chip RAM, ROM, I/O ports...
Example:Intel’s 8051, Motorola’s 6811, Zilog’s Z8 and PIC 16X
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A single chip
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PIN DIAGRAM
8051
Pin Description of the 8051
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1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
RST
(RXD)P3.0
(TXD)P3.1
(T0)P3.4
(T1)P3.5
XTAL2
XTAL1
GND
(INT0)P3.2
(INT1)P3.3
(RD)P3.7
(WR)P3.6
Vcc
P0.0(AD0)
P0.1(AD1)
P0.2(AD2)
P0.3(AD3)
P0.4(AD4)
P0.5(AD5)
P0.6(AD6)
P0.7(AD7)
EA/VPP
ALE/PROG
PSEN P2.7(A15)
P2.6(A14)
P2.5(A13)
P2.4(A12)
P2.3(A11)
P2.2(A10)
P2.1(A9)
P2.0(A8)
8051
(8031)
Pins of 8051
VCC pin 40 :VCC provides supply voltage to the chip. [+5V]
GND pin 20 :ground
XTAL1 and XTAL2 pins 19,18 :
These 2 pins provide external
clock frequency for the operation.
RST pin 9 :reset
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
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C2
30p
F C1
30p
F
XTAL
2
XTAL
1
GN
D
Pins of 8051
EA¯ pin 31 :external access
When the pin is high program fetches to address 0000H-0FFFH
directed to internal ROM and program fetches to address 1000H-
FFFFH are directed to external ROM/EPROM.
When the pin is low all addresses (0000H - FFFFH) fetched by
program are directed to the external ROM/PROM.
PSEN¯ pin 29 :program store enable
It is the active low output control signal used to activate the enable
signal of the external ROM/PROM.
ALE pin 30 :address latch enable
AD0-AD7 are multiplexed. To demultiplex these lines and for
obtaining lower half of an address, an external latch and ALE signal
of 8051 is used.
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Pins of 8051
I/O port pins
The four ports P0, P1, P2, and P3.
Each port uses 8 pins.
All I/O pins are bi-directional.
Port 0 (pins 32-39) used as a multiplexed address/data bus.
Port 1 (pins 1-8) used only as I/O pins.
Port 2 (pins 21-28) used to access external memory when the
address is 16bit wide otherwise port2 is used as an I/O port.
Port 3 (pins 10-17) multifunctional port pins. It can be
programmed to use as I/O or as one of the alternate function. It
includes 2 external interrupts, 2 counter inputs, 2 special data
lines and 2 timing control.
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ARCHITECTURE 8051
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ARCHITECTURE 8051
BLOCK DIAGRAM
Architecture of 8051 Microcontroller Accumulator: 8-bit register. Arithmetic operations.
B Register: 8-bit register. General purpose register.
Program Status Word: Set of flags contains the status information. It is one of the SFR.
Stack Pointer: 8-bit register.
Data Pointer: 16-bit register contains a high byte (DPH) and low byte (DPL). It has been
allotted two addresses in the SFR bank for its two bytes DPH and DPL.
Port 0 to 3 Latches and Drivers: These 4 latches and driver pairs are allotted to each of the 4
on-chip I/O ports. These latches have been allotted addresses in the SFR bank. Using the
allotted address the user can communicate with these ports (P0,P1,P2,P3)
Serial Data Buffer: It contains 2 independent register one of them is transmit buffer, which is a
parallel-in-serial-out register. The other is a receive buffer, which is a serial-in-parallel-out
register. It is one of the SFR.
Timer Registers: Two 16-bit registers. TL0, TH0 represent the lower and higher byte of timer
register 0, similarly TL1, TH1 represent the lower and higher byte of timer register 1.
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Control Registers: It contains control and status information for interrupts
Timing and Control Unit: It derives all the necessary timing at control signals register for
internal operation of the circuit.
Oscillator: It generates the basic timing clock signal for the operation of the circuit using
crystal oscillator.
Instruction Register: This register decodes the opcode of an instruction to be executed and
gives information to the timing and control unit to generate necessary signals on the execution
of instruction.
EPROM and Program Address Register: It provides an on chip EPROM and a mechanism to
internally address it.
RAM and RAM Address Register: It provide internal 128 bytes of RAM and a mechanism to
address it internally.
ALU: It performs 8-bit arithmetic, logical operations over the operands held by temporary
register TMP1 and TMP2. users can’t access these temp. register.
SFR Register Bank: Special Function register range 80H to FFH.
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ADDRESSING MODES OF 8051
ADDRESSING MODES OF 8051
The 8051 provides a total of five distinct addressing modes.
1. Immediate Addressing mode
2. Register Addressing mode
3. Direct Addressing mode
4. Register Indirect Addressing mode
5. Indexed Addressing mode
6. Register Specific Addressing mode
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1) Immediate Addressing Mode
The operand comes immediately after the op-code.
The immediate data must be preceded by the pound sign, "#".
Ex: MOV A, #25H ; load 25H into A
MOV DPTR, #3481H ; DPTR=3481H
2) Register Addressing Mode
Register addressing mode involves the use of registers to hold the data to be manipulated
Ex: MOV A,R0 ; copy the contents of R0 into A
ADD A,R5 ; add the contents of R5 to contents of A
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3) Direct Addressing Mode
It is most often used to access RAM locations 30 - 7FH.
In the direct addressing mode, the data is in a RAM memory location whose
address is known, and this address is given as a part of the instruction
Ex: MOV 56H,A ; save content of A in RAM location 56H
MOV R4,34H ; move contents of RAM location 34H to R4
4) Register Indirect Addressing Mode
A register is used as a pointer to the data.
If the data is inside the CPU, only registers R0 and R1 are used for this.
When RO and R1 are used as pointers they must be preceded by the @ sign.
Ex: MOV A,@R0 ;move the contents of RAM location whose address is held by R0 into A
MOV @R1,B ;move content of B in to RAM location whose address is held by R1
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5) Indexed Addressing Mode
Indexed addressing mode is widely used in accessing data elements of look-up table entries located in the program ROM space of the 8051.
The instruction used for this purpose is : MOVC A, @ A+DPTR
The 16-bit register DPTR and register A are used to form the address of the data element stored in on-chip ROM.
The instruction MOVC is used instead of MOV. "C" means code.
6) Register Specific Addressing Mode
Instructions are specific to the registers such as accumulator or DPTR
Ex: SWAP A ; Swap nibbles within the Accumulator
RAL ; Rotate Accumulator Left
RAR ; Rotate Accumulator Right
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8051 INSTRUCTION SET
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DATA TRANSFER INSTRUCTIONS
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DATA TRANSFER INSTRUCTIONS
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DATA TRANSFER INSTRUCTIONS
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ARITHMETIC OPERATORS
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LOGICAL OPERATIONS
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JUMP & BRANCH INSTRUCTIONS
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8051 TIMER/COUNTER
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SERIAL DATA INPUT/OUTPUT
8051 has a serial data communication circuit that uses
Register Serial port data Buffer (SBUF):
SBUF is physically two registers.
One is write only and is used to hold data to be transmitted out of the 8051 via TXD
Other is read only and holds the received data from external sources via RXD
Register Serial port control (SCON):
Controls data communication
There are four programmable modes for serial data communication that are chosen by setting the SMx bits in SCON.
Register Power mode control (PCON):
Controls data rates and pins RXD & TXD
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SCON
SM0 & SM1: Serial port mode bit0 & bit1
SM2: Multiprocessor communications bit.
Set/clear to enable multiprocessor communications.
REN: Receive Enable bit. set/clear to enable/disable reception.
TB8: Transmitted bit 8.
RB8: Received bit 8.
TI: Transmit interrupt flag.
RI: Receive interrupt flag. 26 February 2014 M.M.Arun Prasath., AP/ECE 33
7 6 5 4 3 2 1 0
SM0 SM1 SM2 REN TB8 RB8 TI RI
SM0 SM1 Mode Description
0 0 0 Shift register; baud=f/12
0 1 1 8-bit UART; baud=set by timer1
1 0 2 9-bit UART; baud=f/32 or f/64
1 1 3 9-bit UART; baud=set by timer1
PCON
SMOD: Serial baud rate modify bit. Set to double baud rate using timer 1 for modes 1,2 & 3.
6-4: Not implemented.
GF1: General purpose user flag bit 1.
GF0: General purpose user flag bit 0.
PD: By setting this bit the microcontroller enters the Power
Down mode
IDL: By setting this bit the microcontroller enters the Idle mode.
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7 6 5 4 3 2 1 0
SMOD - - - GF1 GF0 PD IDL
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INTERRUPTS
Interrupts may be generated by the internal chip operations or provided by the external sources.
5 interrupts are available in 8051
3 are generated automatically by the internal operations: Timer flag 0, Timer flag 1 & Serial port interrupt (RI or TI)
2 are triggered by external signals provided by the circuitry that is connected to pins INT0‾ and INT1‾
Programmer is able to alter control bits in the IE, IP and TCON.
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INTERRUPT ENABLE (IE)
EA: Enable interrupt bit.
Bit 6: not implemented
ET2: future use
ES: Enable serial port interrupt
ET1: Enable Timer 1 overflow interrupt
EX1: Enable external interrupt 1
ET0: Enable Timer 0 overflow interrupt
EX0: Enable external interrupt 0
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7 6 5 4 3 2 1 0
EA -- ET2 ES ET1 EX1 ET0 EX0
Bit 7: not implemented
Bit 6: not implemented
PT2: future use
PS: Priority of serial port interrupt
PT1: Priority of Timer 1 overflow interrupt
PX1: Priority of external interrupt 1
PT0: Priority of Timer 0 overflow interrupt
PX0: Priority of external interrupt 0
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7 6 5 4 3 2 1 0
-- -- PT2 PS PT1 PX1 PT0 PX0
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8051 INTERFACING
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KEYBOARD INTERFACING
4x4 matrix connected with two ports of 8051
Rows to output port columns to input port
If data reads from column is D3-D0 = 1111, no key is pressed
If key press occurred for ex: D3-D0=1011, a key in D2 column has been pressed.
After a key press detected the MC will go through the process of identifying the key.
Grounding each row from D0-D3 it reads the column, if the data read is all 1’s, no key in that row is activated and the process is moved to next row.
After row identification next task to identify column
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KEYBOARD INTERFACING
LCD INTERFACING
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LCD has 14pins: 8 data pins (D0-D7), 3 supply pins (Vcc,VEE,Vss) and 3 control pins(RS,R/W,EN)
When RS=0 the instruction command code register is selected user can send command to clear display, etc.,
When RS=1 the data register is selected the user to send data to be displayed on LCD.
R/W=1 data read from LCD
R/W=0 information written to the LCD
Enable pin used to latch information presented to its data pins.
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LCD INTERFACING
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