Microprocessor 8085 Chapter 1 Microprocessor:-The microprocessor is a semi programmable logic device that can be used to control processes.it can also be used as a data processing device or a computing unit of a computer.8085 is 8 bit microprocessor that can access 8 bits of data and 16 bit address line used to fatch aproximately 64k memory location internally. Difference between microprocessor and microcontroller Microprocessor is an IC which has only the CPU inside them i.e. only the processing powers. These microprocessors don’t have RAM, ROM, and other peripheral on the chip. A system designer has to add them externally to make them functional. Application of microprocessor includes Desktop PC’s, Laptops, notepads etc. Microcontroller has a CPU, in addition with a fixed amount of RAM, ROM and other peripherals all embedded on a single chip. At times it is also termed as a mini computer or a computer on a single chip. Microcontrollers are designed to perform specific tasks. Specific means applications where the relationship of input and output is defined. Depending on the input, some processing needs to be done and output is delivered. For example, keyboards, mouse, washing machine, remote, microwave, cars, bikes, telephone, mobiles, watches, etc. Since the applications are very specific, they need small resources like RAM, ROM, I/O ports etc and hence can be embedded on a single chip. Microprocessor find applications where tasks are unspecific like developing software, games, websites, photo editing, creating documents etc. In such cases the relationship between input and output is not defined. They need high amount of resources like RAM, ROM, I/O ports etc. The clock speed of the Microprocessor is quite high as compared to the microcontroller. Whereas the microcontrollers operate from a few MHz to 30 to 50 MHz, today’s microprocessor operate above 1GHz as they perform complex task.
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Microprocessor 8085
Chapter 1
Microprocessor:-The microprocessor is a semi programmable logic device that can
be used to control processes.it can also be used as a data processing device or a
computing unit of a computer.8085 is 8 bit microprocessor that can access 8 bits of
data and 16 bit address line used to fatch aproximately 64k memory location
internally.
Difference between microprocessor and microcontroller
Microprocessor is an IC which has only the CPU inside them i.e. only the
processing powers. These microprocessors don’t have RAM, ROM, and other
peripheral on the chip. A system designer has to add them externally to make them
functional. Application of microprocessor includes Desktop PC’s, Laptops,
notepads etc.
Microcontroller has a CPU, in addition with a fixed amount of RAM, ROM and
other peripherals all embedded on a single chip. At times it is also termed as a mini
computer or a computer on a single chip. Microcontrollers are designed to perform
specific tasks. Specific means applications where the relationship of input and
output is defined. Depending on the input, some processing needs to be done and
output is delivered. For example, keyboards, mouse, washing machine, remote,
microwave, cars, bikes, telephone, mobiles, watches, etc. Since the applications are
very specific, they need small resources like RAM, ROM, I/O ports etc and hence
can be embedded on a single chip.
Microprocessor find applications where tasks are unspecific like developing
software, games, websites, photo editing, creating documents etc. In such cases the
relationship between input and output is not defined. They need high amount of
resources like RAM, ROM, I/O ports etc.
The clock speed of the Microprocessor is quite high as compared to the
microcontroller. Whereas the microcontrollers operate from a few MHz to 30 to 50
MHz, today’s microprocessor operate above 1GHz as they perform complex task.
Chapter2
Block diagram of 8085 microprocessor:-
Description of block diagram:-
1. ALU:-The ALU performs the actual numerical and logic operation such as
‘add’, ‘subtract’, ‘AND’, ‘OR’ etc.It uses data from memory and from
Accumulator to perform arithmetic operation and always stores result of operation
in Accumulator. The ALU consists of accumulator, flag register and temporary
register.
a. Accumulator: The accumulator is an 8-bit register that is a part of
arithmetic/logic unit (ALU). This register is used to store 8-bit data and to perform
arithmetic and logical operations. The result of an operation is stored in the
accumulator.The accumulator is also identified as register A.
b. Flag registers:-8085 has 8-bit flag register. There are only 5 active flags. Flags
are flip-flops which are used to indicate the status of the accumulator and other
register after the completion of operations. These flip-flops are set or reset
according to the data condition of the results.
c. Timing and control unit:-This unit produces all the timing and control signal for
all the operation. This unit synchronizes all the MP operations with the clock and
generates the control signals necessary for communication between the MP and
peripherals.
3. Instruction register and decoder:-The instruction register and decoder are part of
ALU. When an instruction is fetched from memory, it is loaded in the instruction
register.The decoder decodes the instruction and establishes the sequence of events
to follow.
4. Register array:-The register unit of 8085 consists of Six general-purpose data
registers B, C,D,E,H. Two 16-bit address registers PC (program counter) and SP
(stack pointer),One increment/decrement counter register and one multiplexer
(MUX). The six general-purpose registers are used to store 8-bit data. They can be
combined as register pairs BC, DE, and HL to perform some 16-bit operations.
Stack Pointer:- SP is 16-bit registers used to point the address of data stored in the
stack memory. It always indicates the top of the stack.
Program Counter:- PC is 16-bit register used to point the address of the next
instruction to be fetched and executed stored in the memory.
5. System bus:-
a. Data bus:-It carries ‘data’, in binary form, between MP and other external
units, such as memory. Typical size is 8 or 16 bits.
b. Address bus:-It carries ‘address’ of operand in binary form. Typical size is 16-
bit.
c. Control Bus:-Control Bus are various lines which have specific functions for
coordinating and controlling MP operations.E.g.: Read/Write control line.
6. Interrupt Control:-
Interrupt is a signal, which suspends the routine what the MP is doing, brings the
control to perform the subroutine, completes it and returns to main routine.
E.g. INTR, TRAP, RST 7.5, RST 6.5, RST 5.5
7. Serial I/O Control :-The MP performs serial data input or output (one bit at a
time). In serial transmission, data bits are sent over a single line, one bit at a
time.The 8085 has two signals to implement the serial transmission: SID (serial
input data) and SOD (serial output data).
Pin diagram of 8085 MP:-
Discription of Pin diagram of 8085:-
Address bus:- A15-A8, it carries the most significant 8-bits of memory/IO address.
Data bus:-AD7-AD0, it carries the least significant 8-bit address and data bus.
Control and status signals:-
These signals are used to identify the nature of operation. There are 3 control
signal and 3 status signals.Three control signals are RD, WR & ALE.
RD − This signal indicates that the selected IO or memory device is to be
read and is ready for accepting data available on the data bus.
WR − This signal indicates that the data on the data bus is to be written into
a selected memory or IO location.
ALE − It is a positive going pulse generated when a new operation is started
by the microprocessor. When the pulse goes high, it indicates address.
When the pulse goes down it indicates data.
Three status signals are IO/M, S0 & S1.
IO/M (input/output or Memory):-
This signal is used to differentiate between IO and Memory operations, i.e. when
it is high indicates IO operation and when it is low then it indicates memory
operation.
S1 & S0
These are sort of control singles.These signals are used to identify the type of
current operation.
Power supply
There are 2 power supply signals − VCC & VSS. VCC indicates +5v power
supply and VSS indicates ground signal.
Clock signals
There are 3 clock signals, i.e. X1, X2, CLK OUT.
X1, X2 − A crystal (RC, LC N/W) is connected at these two pins and is
used to set frequency of the internal clock generator. This frequency is
internally divided by 2.8085 requires approximately 3.2MHz of frequency
whereas crystal generate 6.14MHz of frequency.
CLK OUT − This signal is used as the system clock for devices connected
with the microprocessor.
Interrupts & externally initiated signals
Interrupts are the signals generated by external devices to request the
microprocessor to perform a task. There are 5 interrupt signals, i.e. TRAP, RST
7.5, RST 6.5, RST 5.5, and INTR. We will discuss interrupts in detail in interrupts
section.
INTA − It is an interrupt acknowledgment signal.
RESET IN − This signal is used to reset the microprocessor by setting the
program counter to zero.
RESET OUT − This signal is used to reset all the connected devices when
the microprocessor is reset.
READY − This signal indicates that the device is ready to send or receive
data. If READY is low, then the CPU has to wait for READY to go high.
HOLD − This signal indicates that another master is requesting the use of
the address and data buses.
HLDA (HOLD Acknowledge) − It indicates that the CPU has received the
HOLD request and it will relinquish the bus in the next clock cycle. HLDA
is set to low after the HOLD signal is removed.
Serial I/O signals
There are 2 serial signals, i.e. SID and SOD and these signals are used for serial
communication.
SOD (Serial output data line) − The output SOD is set/reset as specified by
the SIM instruction.
SID (Serial input data line) − The data on this line is loaded into
accumulator whenever a RIM instruction is executed.
Applications of microprocessor
o The microprocessor is used in personal computers (PCs).
o The microprocessor is used in LASER printers for good speed and making
automatic photo copies.
o The microprocessors are used in modems, telephone, digital telephone sets,
and also in air reservation systems and railway reservation systems.
o The microprocessor is used in medical instrument to measure temperature and
blood pressure.
o It is also used in mobile phones and television.
o It is used in calculators and game machine.
o It is used in accounting system and data acquisition system.
o It is used in military applications.
o It is also used in traffic light control.
o Microprocessor is used in home appliances such as microwave ovens, washing
machine etc.
Chapter 3
Instruction cycle in 8085 microprocessor :-
Time required to execute and fetch an entire instruction is called instruction cycle.
It consists:
Fetch cycle – The next instruction is fetched by the address stored in program
counter (PC) and then stored in the instruction register.
Decode instruction – Decoder interprets the encoded instruction from
instruction register.
Reading effective address – The address given in instruction is read from
main memory and required data is fetched. The effective address depends on
direct addressing mode or indirect addressing mode.