31. How many machine cycles does 8085 have, mention them
Ans:The 8085 have seven machine cycles. They are
- Opcode fetch
- Memory read
- Memory write
- I/O read
- I/O write
- Interrupt acknowledge
- Bus idle
32. Explain the signals HOLD, READY and SID
Ans:HOLD indicates that a peripheral such as DMA controller is requesting the use of address bus, data bus and control bus. READY is used to delay the microprocessor read or write cycles until a slow responding peripheral is ready to send or accept data.SID is used to accept serial data bit by bit
33. Mention the categories of instruction and give two examples for each category.
Ans:The instructions of 8085 can be categorized into the following five categories
- Data transfer Instructions -MOV Rd,Rs STA 16-bit
- Arithmetic Instructions -ADD R DCR M
- Logical Instructions -XRI 8-bit RAR
- Branching Instructions -JNZ CALL 16-bit
- Machine control Instructions -HLT NOP
34. Explain LDA, STA and DAA instructions
Ans:LDA copies the data byte into accumulator from the memory location specified by the 16-bit address. STA copies the data byte from the accumulator in the memory location specified by 16-bit address. DAA changes the contents of the accumulator from binary to 4-bit BCD digits.
35. Explain the different instruction formats with examples
Ans:The instruction set is grouped into the following formats
- One byte instruction -MOV C,A
- Two byte instruction -MVI A,39H
- Three byte instruction -JMP 2345H
36. What is the use of addressing modes, mention the different types
Ans:The various formats of specifying the operands are called addressing modes, it is used to access the operands or data. The different types are as follows
- Immediate addressing
- Register addressing
- Direct addressing
- Indirect addressing
- Implicit addressing
37. What is the use of bi-directional buffers?
Ans:It is used to increase the driving capacity of the data bus. The data bus of a microcomputer system is bi-directional, so it requires a buffer that allows the data to flow in both directions.
38. Give the register organization of 8085
Ans:
| W(8) |
Temp. Reg |
| Z(8) |
Temp. Reg |
| B(8) |
Register |
| C(8) |
Register |
| D(8) |
Register |
| E(8) |
Register |
| H(8) |
Register |
| L(8) |
Register |
| Stack Pointer |
(16) |
| Program Counter |
(16) |
39. Define stack and explain stack related instructions
Ans:The stack is a group of memory locations in the R/W memory that is used for the temporary storage of binary information during the execution of the program. The stack related instructions are PUSH & POP
40. Why do we use XRA A instruction
Ans:The XRA A instruction is used to clear the contents of the Accumulator and store the value 00H.
41. Compare CALL and PUSH instructions
Ans:
| CALL |
PUSH |
|
1.When CALL is executed the microprocessor automatically stores the 16-bit address of the instruction next to CALL on the stack.
2.When CALL is executed the stack pointer is decremented by two
|
1.PUSH The programmer uses the instruction to save the contents of the register pair on the stack
2. When PUSH is executed the stack pointer is decremented by two
|
42. What is Microcontroller and Microcomputer
Ans:Microcontroller is a device that includes microprocessor; memory and I/O signal lines on a single chip, fabricated using VLSI technology. Microcomputer is a computer that is designed using microprocessor as its CPU. It includes microprocessor, memory and I/O.
43. Define Flags
Ans:The flags are used to reflect the data conditions in the accumulator. The 8085 flags are S-Sign flag, Z-Zero flag, AC-Auxiliary carry flag, P-Parity flag, CYCarry flag, D7 D6 D5 D4 D3 D2 D1 D0
44. How does the microprocessor differentiate between data and instruction?
Ans:When the first m/c code of an instruction is fetched and decoded in the instruction register, the microprocessor recognizes the number of bytes required to fetch the entire instruction. For example MVI A, Data, the second byte is always considered as data. If the data byte is omitted by mistake whatever is in that memory location will be considered as data & the byte after the “data” will be
treated as the next instruction.
45. Compare RET and POP
Ans:
| RET |
POP |
|
1.RET transfers the contents of the top two locations of the stack to the PC
2.When RET is executed the SP is incremented by two
3.Has 8 conditional RETURN instructions
|
1.POP transfers the contents of the top two locations of the stack to the specified register pair
2. When POP is executed the SP is incremented by two
3.No conditional POP instructions
|
1 2 3 4 5 6 7