1. 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
2. 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
Instructions -ADD R DCR M
Instructions -XRI 8-bit RAR
Instructions -JNZ CALL 16-bit
Machine control Instructions -HLT NOP
3 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.
4. 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
5. 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
6. 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
7. 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
8. 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.
9. 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.
10. 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.
11. What is assembler?
Ans:The assembler translates the assembly language program text which is given as input to the assembler to their binary equivalents known as object code. The time required to translate the assembly code to object code is called access time. The assembler checks for syntax errors & displays them before giving the object code.
12. What is loader?
Ans:The loader copies the program into the computer’s main memory at load time and begins the program execution at execution time.
13. What is linker?
Ans:A linker is a program used to join together several object files into one large object file. For large programs it is more efficient to divide the large program modules into smaller modules. Each module is individually written, tested & debugged. When all the modules work they are linked together to form a large functioning program.
14. What is interrupt service routine?
Ans:Interrupt means to break the sequence of operation. While the CPU is executing a program an interrupt breaks the normal sequence of execution of instructions & diverts its execution to some other program. This program to which the control is transferred is called the interrupt service routine. 50.What are the various programmed data transfer methods?
Ans: i) Synchronous data transfer ii) Asynchronous data transfer iii) Interrupt driven data transfer
15. What is synchronous data transfer?
Ans:It is a data method which is used when the I/O device and the microprocessor match in speed. To transfer a data to or from the device, the user program issues a suitable instruction addressing the device. The data transfer is completed at the end of the execution of this instruction.
16. What is asynchronous data transfer?
Ans:It is a data transfer method which is used when the speed of an I/O device does not match with the speed of the microprocessor. Asynchronous data transfer is also called as Handshaking.
17. What are the basic modes of operation of 8255?
Ans: There are two basic modes of operation of 8255, They are:
1. I/O mode. 2. BSR mode.
In I/O mode, the 8255 ports work as programmable I/O ports, while In BSR mode only port C (PC0-PC7) can be used to set or reset its individual port bits. Under the IO mode of operation, further there are three modes of operation of 8255, So as to support different types of applications, viz. mode 0, mode 1 and mode 2.
Mode 0 – Basic I/O mode
Mode 1 – Strobed I/O mode
Mode 2 – Strobed bi-directional I/O.
18. Write the features of mode 0 in 8255?
Ans:1. Two 8-bit ports (port A and port B) and two 4-bit ports (port C upper and lower) are available. The two 4-bit ports can be combined used as a third 8-bit port. 2. Any port can be used as an input or output port. 3.Output ports are latched. Input ports are not latched. 4. A maximum of four ports are available so that overall 16 I/O configurations are possible.
19. What are the features used mode 1 in 8255?
Ans:Two groups – group A and group B are available for strobed data transfer.
1. Each group contains one 8-bit data I/O port and one 4-bit control/data port. 2. The 8-bit data port can be either used as input or output port. The inputs and outputs both are latched. 3. Out of 8-bit port C, PC0-PC2 is used to generate control signals for port B and PC3=PC5 are used to generate control signals for port A. The lines PC6, PC7 may be used as independent data lines.
20. What are the signals used in input control signal & output control signal?
Ans: Input control signal
STB (Strobe input)
IBF (Input buffer full)
Output control signal
OBF (Output buffer full)
ACK (Acknowledge input)