Microcontroller 8051

Contents: Introduction Block Diagram and Pin Description of the 8051 Registers Memory mapping in 8051 Stack in the 8051 I/O Port Programming Timer Interrupt

Why do we need to learn Microprocessors/controllers? The microprocessor is the core of computer systems. Nowadays many communication, digital entertainment, portable devices, are controlled by them. A designer should know what types of components he needs, ways to reduce production costs and product reliable.

Different aspects of a microprocessor/controller Hardware :Interface to the real world Software :order how to deal with inputs

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

Microprocessors: General-purpose microprocessor 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 Data Bus CPU General-Purpose Micro-processor Serial COM Port I/O Port Intel’s x86: 8086,8088,80386,80486, Pentium Motorola’s 680x0: 68000, 68010, 68020,68030,6040 RAM ROM Timer Address Bus General-Purpose Microprocessor System

Microcontroller : A single chip A smaller computer On-chip RAM, ROM, I/O ports... Example：Motorola’s 6811, Intel’s 8051, Zilog’s Z8 and PIC 16X CPU RAM ROM A single chip Serial COM Port I/O Port Timer Microcontroller

Microprocessor vs. Microcontroller 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 versatility 多用途的: any number of applications for PC

Embedded System 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：printer, keyboard, video game player processor 整合到整個系統中, 你只看到此系統的外觀, 應用, 感覺不到有 processor 在其中. Embedded system 通常只有一項應用, 而 PC 有許多 applications (game, accounting, fax, mail...) A printer is an example of embedded system since the processor inside it performs one task only.

Three criteria in Choosing a Microcontroller 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 availability of software development tools assemblers, debuggers, C compilers, emulator, simulator, technical support wide availability and reliable sources of the microcontrollers.

Block Diagram External interrupts On-chip ROM for program code Timer/Counter Interrupt Control On-chip RAM Timer 1 Counter Inputs Timer 0 CPU Serial Port Bus Control 4 I/O Ports OSC P0 P1 P2 P3 TxD RxD Address/Data

Pin Description of the 8051 8051  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 

Vcc provides supply voltage to the chip. The voltage source is +5V. Pins of 8051（1/4） Vcc（pin 40）： Vcc provides supply voltage to the chip. The voltage source is +5V. GND（pin 20）：ground XTAL1 and XTAL2（pins 19,18）

Figure (a). XTAL Connection to 8051 Using a quartz crystal oscillator We can observe the frequency on the XTAL2 pin. C2 30pF C1 XTAL2 XTAL1 GND 

It is an input pin and is active high（normally low）. Pins of 8051（2/4） RST（pin 9）：reset It is an input pin and is active high（normally low）. 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

Figure (b). Power-On RESET Circuit Vcc + 10 uF 31 EA/VPP X1 30 pF 19 11.0592 MHz 8.2 K X2 18 30 pF RST 9 

/EA（pin 31）：external access Pins of 8051（3/4） /EA（pin 31）：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 ＆ ALE are used for external ROM. For 8051, /EA pin is connected to Vcc. “/” means active low. /PSEN（pin 29）：program store enable This is an output pin and is connected to the OE pin of the ROM.

ALE（pin 30）：address latch enable Pins of 8051（4/4） ALE（pin 30）：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.

Ex：P0.0 is the bit 0（LSB）of P0 Ex：P0.7 is the bit 7（MSB）of P0 Pins of I/O Port The 8051 has four I/O ports Port 0 （pins 32-39）：P0（P0.0～P0.7） Port 1（pins 1-8） ：P1（P1.0～P1.7） Port 2（pins 21-28）：P2（P2.0～P2.7） Port 3（pins 10-17）：P3（P3.0～P3.7） Each port has 8 pins. Named P0.X （X=0,1,...,7）, P1.X, P2.X, P3.X Ex：P0.0 is the bit 0（LSB）of P0 Ex：P0.7 is the bit 7（MSB）of P0 These 8 bits form a byte. Each port can be used as input or output (bi-direction). Program is to read data from P0 and then send data to P1 

Hardware Structure of I/O Pin Each pin of I/O ports Internal CPU bus：communicate with CPU A D latch store the value of this pin D latch is controlled by “Write to latch” Write to latch＝1：write data into the D latch 2 Tri-state buffer： TB1: controlled by “Read pin” Read pin＝1：really read the data present at the pin TB2: controlled by “Read latch” Read latch＝1：read value from internal latch A transistor M1 gate Gate=0: open Gate=1: close

D Latch:

A Pin of Port 1 P0.x 8051 IC Read latch Vcc TB2 Load(L1) P1.X pin D Q Clk Q Vcc Load(L1) Read latch Read pin Write to latch Internal CPU bus M1 P1.X pin P1.X TB1 TB2 P0.x 8051 IC

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 pin P1.X TB2 2. output pin is Vcc 1. write a 1 to the pin 1 output 1 TB1 8051 IC

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 pin P1.X TB2 2. output pin is ground 1. write a 0 to the pin output 0 1 TB1 8051 IC

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 2. MOV A,P1 external pin=High TB2 write a 1 to the pin MOV P1,#0FFH 1 1 TB1 3. Read pin=1 Read latch=0 Write to latch=1 8051 IC

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 2. MOV A,P1 external pin=Low TB2 write a 1 to the pin MOV P1,#0FFH 1 TB1 3. Read pin=1 Read latch=0 Write to latch=1 8051 IC

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.

A Pin of Port 0 P1.x 8051 IC Read latch TB2 P0.X pin Internal CPU bus D Q Clk Q Read latch Read pin Write to latch Internal CPU bus M1 P0.X pin P1.X TB1 TB2 P1.x 8051 IC

Port 0 with Pull-Up Resistors DS5000 8751 8951 Vcc 10 K Port 0

Port 3 Alternate Functions 17 RD P3.7 16 WR P3.6 15 T1 P3.5 14 T0 P3.4 13 INT1 P3.3 12 INT0 P3.2 11 TxD P3.1 10 RxD P3.0 Pin Function P3 Bit 

RESET Value of Some 8051 Registers: PC 0000 ACC 0000 B 0000 PSW 0000 SP 0007 DPTR 0000 RAM are all zero. 

Some 8-bitt Registers of the 8051 A B R0 R1 R3 R4 R2 R5 R7 R6 DPH DPL PC DPTR Some 8051 16-bit Register Some 8-bitt Registers of the 8051

Memory mapping in 8051 ROM memory map in 8051 family 4k 8k 32k 0000H 0FFFH 1FFFH 7FFFH 8751 AT89C51 8752 AT89C52 4k 8k 32k DS5000-32 from Atmel Corporation from Dallas Semiconductor

RAM memory space allocation in the 8051 7FH 30H 2FH 20H 1FH 17H 10H 0FH 07H 08H 18H 00H Register Bank 0 (Stack) Register Bank 1 Register Bank 2 Register Bank 3 Bit-Addressable RAM Scratch pad RAM

Stack in the 8051 7FH 30H 2FH 20H 1FH 17H 10H 0FH 07H 08H 18H 00H Register Bank 0 (Stack) Register Bank 1 Register Bank 2 Register Bank 3 Bit-Addressable RAM Scratch pad RAM The register used to access the stack is called SP (stack pointer) register. The stack pointer in the 8051 is only 8 bits wide, which means that it can take value 00 to FFH. When 8051 powered up, the SP register contains value 07.

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.

TMOD Register:

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.

TCON Register:

Interrupt :

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.