©SREEYUSH SUDHAKARAN,VVCET(sree.eceengg@gmail.com)
1.Can an RC circuit be used as clock source for 8085?
Ans: ya it can be used as clock source.
one important advantage of RC clock is that it can avoid RACE AROUND condition by
producing sharp edged pulses.
2.Which interrupt has the highest priority?
Ans: The TRAP is nonmaskable interrupt know as NMI. It has highest priority among the
interrupt signal because; it need not be enabled and cannot be disabled. It is level-and
edge-sensitive, meaning that the input should go high and stay high to be acknoledged.It
cannot be acknowledged again until it makes a transition from high to low to high.
3. What are machine cycle, instruction cycle and T-state?
ANS1: Machine Cycle: The necessary steps to a fetch, a read or a write operation
constitute a Machine cycle. It includes of 3-6 T-states.
Instruction Cycle: The necessary steps that a CPU carries out to fetch an instruction and
necessary data from the memory and to execute it constitute an Instruction Cycle. 8085
instruction cycle consist of 1-6 machine cycle.
T-state: One sub-division of an operation performed in one clock cycle is called a T-state.
4. What are Hardware interrupts?
Ans: TRAP, RST7.5, RST6.5, RST5.5, INTR
5. In 8085 name the 16 bit registers?
Ans: In general purpose register it contains 6 register b,c,d,e,h,l. each register has 8 bit,
the combination of two register make 16bit. program counter(16),stack pointer(16)
6. Difference between memory mapped IO and IO mapped IO?
ANS: Memory mapped IO is one where the processor and the IO device share the same
memory location(memory) while IO mapped IO is one where the processor and the IO
device have different memory located to each other.
7. What is Program counter?
Program counter holds the address of either the first byte of the next instruction to be
fetched for execution or the address of the next byte of a multi byte instruction, which has
not been completely fetched. In both the cases it gets incremented automatically one by
one as the instruction bytes get fetched. Also Program register keeps the address of the
next instruction.
8. Define interrupt?
Interrupt is an signal sent or given to the processor in order to interrupt or to stop the
current process/execution and transfer the control to the specified process in order to
perform particular task.
There are 3 types of programmable interrupts in 8085.. int 5.5, int 6.5, int 7.5 and one
hardware interrupt TRAP
TRAP signal given to the processor halts the current execution and the control is been
transferred to the ISR(interrupt service subroutine register). And the programmable
interrupts are one which can be accessed programatically by setting the bit pattern in the
registar
These intrrupts are used to transfer the control to the periphearal devices.. when the
normal execution is in process.
Interrupt is nothing but a DELAY caused during the processing of data, it may be transfer
of data,
input,output.
they are of many types
1)program interrupt
2)instruction interrupt
3)software interrupt
4>hard ware interrupt.
9. What is clock frequency for 8085?
basically its 3 Mhz but to get this frequency crystal should have 6 Mhz internal frequency
due to RL & RC crystals..
10. Which Stack is used in 8085?
Stack is a collection of continuous
memory location which is used when interrupt occurs in computer. microprocessor sends
the instruction from register to stack by PUSH operation and other instruction is executed.
after finishing this instruction the microprocessor brings that instruction by POP operation
and executes. Stack is associated with stack pointer register, which is 16 bit. It maintains
the address of top stack.
11. What are the various flags used in 8085?
there are 5 flags of intel 8085 are:
Carry flag(CY),
parity flag(P),
Auxiliary Carry flag(AC),
Zero Flag(Z),
Sign flag(S).
12. What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high and
low are normal logic levels & high impedance state is electrical open circuit conditions. Tristate logic has a third line called enable line.