1. Presented by Sadhish Prabhu
MICROCONTROLLER
Presented by
Sadhish Prabhu

2. Contents Introduction to microcontrollers Architecture details
Pin configuration

4. General-Purpose Microprocessor System
Introduction
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

5. 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

6. 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

7. 3 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.

8. MCS-51 “Family” of Microcontrollers
8051 introduced by Intel in late 1970s
Now produced by many companies in many variations
The most pupular microcontroller – about 40% of market share
8-bit microcontroller

9. Comparison of the 8051 Family Members
Feature
ROM (program space in bytes) 4K K K
RAM (bytes)
Timers
I/O pins
Serial port
Interrupt sources

12. FEATURES

13. On-Chip DATA Memory: RAM
Internal RAM

14. Registers Four Register Banks Each bank has R0-R7 Bank 3 Bank 2 Bank 118
Four Register Banks
Each bank has R0-R7
Bank 3 17 10
Bank 2 0F 08
Bank 1 07 06 05 04 03 02 01 00 R7 R6 R5 R4 R3 R2 R1 R0
Bank 0

15. Bit Addressable Memory2F 2E 2D 2C 2B 2A 29 28
20h – 2Fh (16 locations X 8-bits = 128 bits) 7F 78 1A 10 0F 08 07 06 05 04 03 02 01 00
Bit addressing:
mov C, 1Ah or
mov C, 23h.2 27 26 25 24 23 22 21 20

16. Special Function Registers
DATA registers
CONTROL registers
Timers
Serial ports
Interrupt system
Analog to Digital converter
Digital to Analog converter
Etc.
Addresses 80h – FFh
Direct Addressing used to access SFRs

17. 8051 CPU Registers A (Accumulator) B PSW (Program Status Word)
SP (Stack Pointer)
PC (Program Counter)
DPTR (Data Pointer)
Used in assembler instructions

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

26. 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.

27. Pin Description of the 8051 8051 (8031)  1 2 3 4 5 6 7 8 9 10 11 1213 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) 

28. Pins of 8051 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）：
These 2 pins provide external clock.
Way 1：using a quartz crystal oscillator
Way 2：using a TTL oscillator
1MHz to 16 MHz

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

30. XTAL Connection to an External Clock Source
Using a TTL oscillator
XTAL2 is unconnected. NC
EXTERNAL
OSCILLATOR
SIGNAL
XTAL2
XTAL1
GND

31. Pins of 8051 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
Way 1：Power-on reset circuit
Way 2：Power-on reset with debounce

32. Pins of 8051 /EA（pin 31）：external access
There is no on-chip ROM in 8031 and
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.

33. Pins of 8051 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.

34. 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.
However, for a programmer, it is the same to program P0, P1, P2 and P3.
All the ports upon RESET are configured as output.

35. Port 0（pins 32-39） P0 is an open drain.
Open drain is a term used for MOS chips in the same way that open collector is used for TTL chips. 
When P0 is used for simple data I/O we must connect it to external pull-up resistors.
Each pin of P0 must be connected externally to a 10K ohm pull-up resistor.
With external pull-up resistors connected upon reset, port 0 is configured as an output port.
Open drain is a term used for MOS chips in the same way that open collector is used for TTL chips.

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

37. Dual Role of Port 0
When connecting an 8051/8031 to an external memory, the 8051 uses ports to send addresses and read instructions.
8031 is capable of accessing 64K bytes of external memory.
16-bit address：P0 provides both address A0-A7, P2 provides address A8-A15.
Also, P0 provides data lines D0-D7.
When P0 is used for address/data multiplexing, it is connected to the 74LS373 to latch the address.
There is no need for external pull-up resistor.

38. ALE Pin
The ALE pin is used for de-multiplexing the address and data by connecting to the G pin of the 74LS373 latch.
When ALE=0, P0 provides data D0-D7.
When ALE=1, P0 provides address A0-A7.
The reason is to allow P0 to multiplex address and data.

39. Port 2（pins 21-28）
Port 2 does not need any pull-up resistors since it already has pull-up resistors internally.
In an 8031-based system, P2 are used to provide address A8-A15.

40. Port 3 Alternate Functions17 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 

41. Reference