A microprocessor is a semiconductor chip fabricated with entire central processing unit (CPU) on it. It is a programmable device that accepts binary data from an input device, processes the data according to the instructions stored in the memory and provides results as output. Basically microprocessor performs two functions - (a) Fetches an instruction from the memory and (b) Performs the operation specified by the instruction. There are special inputs to the microprocessor called interrupts. External devices use these interrupts to get the microprocessor attention. A micro computer can be built by using 8085 microprocessor along with many other chips such as 8155, 8255, 8279, 8253, 8257, 8259, 8251 etc. 8085 microprocessor is 8-bit microprocessor which has 8-bit data registers where as 8086 is a 16-bit microprocessor.
In 8085, if the clock frequency is 5 MHz, the time required to execute an instruction of 18 T-states is :
3.6 μ sec
A T-state is one clock period, so the whole calculation is two lines.
Step 1 — find the clock period.
\(T=\dfrac{1}{f}=\dfrac{1}{5\times10^{6}}=0.2\times10^{-6}\ \text{s}=0.2\ \mu\text{s}\)
Step 2 — multiply by the number of T-states.
\(t=18\times0.2\ \mu\text{s}=3.6\ \mu\text{s}\)
which is option 2.
The vocabulary the 8085 uses for timing is worth fixing, because these three terms are constantly confused:
| Term | Meaning |
|---|---|
| T-state | One clock period — the smallest unit of time |
| Machine cycle | The time to complete one bus operation (opcode fetch, memory read, memory write, I/O read, I/O write); 3 to 6 T-states |
| Instruction cycle | The total time for one complete instruction; 1 to 5 machine cycles |
An opcode fetch takes 4 T-states (6 for some instructions), while a memory read or write takes 3. An 18 T-state instruction is therefore a long one — CALL, for example, is 18 T-states in five machine cycles, since it must fetch a three-byte instruction and then push the return address onto the stack.
One caution about the word "clock". The 8085 contains an internal divide-by-two, so a crystal connected across X1 and X2 runs at twice the operating frequency — a 6 MHz crystal gives a 3 MHz internal clock. Here the question specifies the clock frequency itself as 5 MHz, so it is the operating frequency and no halving applies. Had it said "crystal frequency", the answer would have been double, at 7.2 μs.
The general form worth memorising :
\(\text{Execution time}=\dfrac{\text{Number of T-states}}{\text{Clock frequency}}\)
This is the standard route to computing software delay loops, where the T-state counts of DCR, JNZ and the rest are added up and multiplied by the clock period to obtain the delay produced.
Hence, the execution time is 3.6 μs.
Similar Questions
A microprocessor is a semiconductor chip fabricated with entire central processing unit (CPU) on it. It is a programmable device that accepts binary data from an input device, processes the data according to the instructions stored in the memory and provides results as output. Basically microprocessor performs two functions - (a) Fetches an instruction from the memory and (b) Performs the operation specified by the instruction. There are special inputs to the microprocessor called interrupts. External devices use these interrupts to get the microprocessor attention. A micro computer can be built by using 8085 microprocessor along with many other chips such as 8155, 8255, 8279, 8253, 8257, 8259, 8251 etc. 8085 microprocessor is 8-bit microprocessor which has 8-bit data registers where as 8086 is a 16-bit microprocessor.
The following 8051 assembly program is given. Answer the questions based on it.
Line No. Mnemonics 1 MOV SP, #4F H 2 SET B PSW.3 3 MOV R0, #25H 4 MOV R1, #0AH 5 MOV R2, #06H 6 PUSH 8 7 PUSH 9 8 PUSH 0AH . . . V V 20 POP 8 $D_7$ $D_6$ $D_5$ $D_4$ $D_3$ $D_2$ $D_1$ $D_0$ In 8255 programmable peripheral interface device, if the port A and port B are to be set in a hand shake mode along with port C, what are the bits in the 8 bit control word to be set as 0 1 0.
The number system for the machine code of the microprocessor 8085 is
Which of the options in a multipurpose instruction used to implement the interrupt of 8085 and serial data input ?
Both 8155 and 8255 programmable peripheral interface ICs have the following common features :
(i) Programmable I/Os
(ii) Either port A or Port B can be set as either input or output ports.
(iii) One 14-bit down counter
(iv) AD0 – AD7 are multiplexed address/datalines.Each instruction in an assembly program has the following fields :
(i) Lable field
(ii) Operand field
(iii) Comment field
(iv) Mnemonic fieldPlease write the proper sequence of fields :
The mnemonic of 8085 processor indicate :
List – I List – II a. RLC i. Rotate Accumulator Right through carry b. RRC ii. Rotate Accumulator Left through carry c. RAR iii. Rotate Accumulator Left d. RAL iv. Rotate Accumulator Right Codes :
Match the following :
List – I (Pin terminals) List – II (Applications) a. SID, SOD i. Wait state b. READY ii. Serial data transfer c. TRAP iii. Address Latch Control d. ALE iv. Interrupt Codes :
Assertion (A) : In serial communication system, when the transmission of data goes in both ways, it is called full-duplex system. Now if two micro processors are connected in full duplex mode, the amount of data transmitted will be double to the amount of data in half-duplex mode connection.
Reason (R) : When the transmission of data goes in one way, it is called half-duplex system and when the data moves in both ways, it is called full duplex system.
Important Questions from Microprocessors
An 8086 address bus is a/an _____ -bit bus
Program counter for any counter:
In the pin out configuration of the 8085 microprocessor, the sequential input data is represented by
Which of the following functions is not performed by a microprocessor?
Match the columns.
Pin
Description
a. D 0-D 7
1. Reset Input
b. RESET
2. Data Lines
c. A 0,A 1
3. Internal Address
