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(1)Why microcontrollers are more in use than
microprocessors?Solution:A microcontroller has a combination of all
the following stuff on a single chip:
Microcontroller = CPU + Peripherals + MemoryPeripherals = Ports
+ Clock + Timers + UARTS + ADC +LCD drivers + D
AC + other stuffMemory = EEPROM + SRAM+ EPROM + FLASH
A microprocessor is just a CPU. If a system designer using a
general purpose register such as Pentium or the 86 family must add
RAM, ROM, and I/O ports and timers externally to make them
functional. This addition of external peripheral makesthe system
bulkier and much more expensive. A microcontroller is a
specializedform of microprocessor that is designed to be
self-sufficient and cost-effective, where a microprocessor is
typically designed to be general purpose. Microcontrollers are
frequently found in automobiles, office machines, toys, and
appliances.The microcontroller is the integration of a number of
useful functions into a single IC package. These functions are: The
ability to execute a stored set of instructions to carry out user
defined ta
sks.
The ability to be able to access external memory chips to both
read and write data from and
to the memory. discrete input and output bits, allowing control
or detection of the logic stateof an individual package pin.
In-circuit programming and debugging support. Also, a
microcontroller is part of an embedded system, which is essentially
thewhole circuit board. Ex- intercom, telephone, security system,
FAX machine, Lighting control, cellular phone, and lots of home
appliances, and automation of machine lots of stuff that make our
life easier fast.
A fixed amount of on-chip ROM, RAM, and number of I/O ports in
microcontroller makes them ideal for many applications in which
cost and space are critical. In many applications such as TV remote
control, there is no need of computing powerof 86 or even 8086
microprocessor.(2)What are the minimum hardware components required
for 8051 to work with its internal ROM? Also show their
connections?solution:
PART:B(2)What are the addressing modes of 8051? How many types
of instructions are their?Solution:The CPU can access data in
various ways. It data could be in a register or be pr
ovided as an immediate value. The 8051 provides a total of five
distinct addressing modes.1. Immediate addressing mode2. register
addressing mode3. direct addressing mode4.register addressing
mode5. indexed addressing mode
Immediate addressing mode:In this addressing mode, the source
operand is constant. In immediate addressingmode, the operand comes
immediately. The immediate data must be preceded by thepound sign #
sign.the followings instruction are used in these addressing
mode:
MOV A, #25H ; load 25H into accumulator AMOV R4, #62H ;load the
decimal value 62 into R4MOV B, #40H ;load 40H into B
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MOV DPTR, #4521H ; DPTR= 4521HSince the DPTR register is of
16-bit, it can also be accessed as two 8-bit registers, DPH and
DPL, where DPH is high byte and DPL is the low byte.MOV DPTR,
#2553H is same as the,MOV DPL, #53HMOV DPH, # 25Hwe can use the EQU
directive to access immediate data as shown below:
COUNT EQU 30... ..MOV R4, #COUNT ; R4= 1E(30=1EH)MOV DPTR,
#MYDATA ; DPTR=200Hto send the data to port to 8051 ports.Ex: MOV
P1, #55HRegister addressing mode:register addressing mode involves
the use of register to hold the data to be manipulated. Ex:-MOV A,
RO ; Copy the contents of RO in AMOV R2, A ; Copy the contents of A
in ROADD A, R5
ADD R5, Ain this mode the source and destination register must
be the same size otherwiseit will shows errorIn this we can move
data between the and Rn (for n= 0 to 7) but movement of between Rn
register is not allowed.Direct addressing mode:In the Direct
addressing mode , the data is in RAM memory location whose
addressis known , and this address is given as a part of the
instruction. Compare withthe immediate addressing mode , in which
the pperand itself provide with the instruction. the # sign
distinguishes between the two modes. Ex:-MOV RO, 40HMOV 56H, AMOV
R4, 7F
the RAM locations 0 to 7 are allocated to bank 0 registers
R0-R7. these registercan be accessed in two ways,MOV A, 4or, MOV A,
R4See the following code ;
MOV R2, #5MOV A,2MOV B,2MOV 7,2 ; Copy R2 to R7
;since MOV R7, R2 is invalidAlthough it is easier to use the
names R0-R7 than their memory addresses, RAM locations 30H to 7FH
can not be accessed in any way other than by their addresses,since
they have no names.Register indirect addressing mode:In the
register addressing mode , aregister is used as a pointer to the
data. ifthe data is inside the CPU, only register R0 and R1 are
used for this purpose.When R0-R1 are used to hold the address of
RAM locations, they must be precededby the @ sign, as shown
below,MOV A,@R0 ;move contents of RAM locations whose
; address is held by R0 into AIndexedr addressing mode:Indexed
addressing mode is used in accessing data elements of look-up table
located in the programROM space of the 8051.the instruction used
for this purpose is MOV A, @+DPTR. The16-bit register DPTR and
register A are used to form the address of the data ele
ment stored on-chip ROM.
