What is program counter? How it is useful in program execution ?
The program counter keeps track of program execution. To execute a program the starting address of the program is loaded in program counter. The PC sends out an address to fetch a byte of instruction from memory and increments its content automatically.
Define opcode and operand ?
Opcode(operation code) is the part of an instruction that identifies a specific operation. Operand is a part of instruction that represents a value on which the instruction acts.
How the 8085 processor differentiates a memory access and I/O access ?
The memory access and I/O access is differentiated using IO/M signal. The 8085 processor asserts IO/M low for memory operation and high for I/O operations.
When the 8085 processor checks for an interrupt ?
In the second T-state of the last machine cycle of every instruction, the 8085 processor checks whether an interrupt request is made or not.
Why interfacing is needed for I/O devices ?
Generally I/O devices are slow devices. Therefore the speed of I/O devices does not match with the speed of microprocessor. And so an interface is provided between system bus and I/O devices.
What is interrupt I/O ?
If the I/O device initiate the data transfer through interrupt then the I/O is called interrupt driven I/O.
What is a port ?
The port is a buffered I/O, which is used to hold the data transmitted from the microprocessor to I/O devices and vice versa.
What is the need for interrupt controller ?
The interrupt controller is employed to expand the interrupt inputs. It can handle the interrupt request from various devices and allow one by one to the processor.
What is synchronous data transfer scheme ?
For synchronous data transfer scheme, the processor does not check the readiness of the device after a command have been issued for read/write operation. For this scheme the processor will request the device to get ready and then read/write to the device immediately after the request.
What is asynchronous data transfer scheme ?
In asynchronous data transfer scheme, first the processor sends a request to the device for read/write operation. Then the processor keeps on polling the status of the device. Once the device is ready, the processor executes a data transfer instruction to complete the process.