46. 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.
47. 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.
48. 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.
49. 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
56. What are the signals used in input control signal & output control signal?
Ans: Input control signal
- STB (Strobe input)
- IBF (Input buffer full)
- INTR(Interrupt request)
Output control signal
- OBF (Output buffer full)
- ACK (Acknowledge input)
- INTR(Interrupt request)
57. What are the features used mode 2 in 8255?
Ans:The single 8-bit port in-group A is available.
1. The 8-bit port is bi-directional and additionally a 5-bit control port is available.
2. Three I/O lines are available at port C, viz PC2-PC0.
3. Inputs and outputs are both latched.
4. The 5-bit control port C (PC3=PC7) is used for generating/accepting handshake signals for the 8-bit data transfer on port A.
58. What are the modes of operations used in 8253?
Ans:Each of the three counters of 8253 can be operated in one of the following six modes of operation.
1. Mode 0 (Interrupt on terminal count)
2. Mode 1 (Programmable monoshot)
3. Mode 2 (Rate generator)
4. Mode 3 (Square wave generator)
5. Mode 4 (Software triggered strobe)
6. Mode 5 (Hardware triggered strobe)
59. What are the different types of write operations used in 8253?
Ans:There are two types of write operations in 8253
(1) Writing a control word register
(2) Writing a count value into a count register
The control word register accepts data from the data buffer and initializes the counters, as required. The control word register contents are used for
(a) Initializing the operating modes (mode 0-mode4)
(b) Selection of counters (counter 0- counter 2)
(c) Choosing binary /BCD counters
(d) Loading of the counter registers.
The mode control register is a write only register and the CPU cannot read its contents.
60. Give the different types of command words used in 8259a?
Ans:The command words of 8259A are classified in two groups
1. Initialization command words (ICWs)
2. Operation command words (OCWs)
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