The memory mapping is the process of interfacing memories to microprocessor and allocating addresses to each memory locations.
What is opcode fetch cycle ?
The opcode fetch cycle is a machine cycle executed to fetch the opcode of an instruction stored in memory. Each instruction starts with opcode fetch machine cycle.
What are the instructions used to control the interrupts ?
What is polling ?
In polling, the microprocessor’s software simply checks each of the I/O devices every so often. During this check, the microprocessor tests to see if any device needs servicing.
What are the different types of interrupts ?
Hardware interrupts - The interrupts where the CPU pins are used to receive interrupt requests, are called hardware interrupts.
Software interrupts - This interrupt is caused by the execution of the instruction. These are special instructions supported bythe microprocessor.
What are the types of hardware interrupts ?
Difference between memory mapped I/o and I/O mapped I/o ?
Memory mapped I/O
In this device address is 16- bit.
MEMR and MEMW control signals are used to control read and write I/O operations.
Instructions available are LDA,STA,MOV R,M , ADD M etc
Data transfer is between any register and I/O device.
Decoding 16-bit address may require more hardware.
I/O mapped I/O
In this device address is 8-bit.
IOR and IOW control signals are used to control read and write I/O operations.
Instructions available are IN and OUT.
Data transfer is between accumulator and I/O device.
Decoding 8-bit address will require less hardware.
Describe the function of the following pins in 8085 ?
a) READY b) ALE c) IO/M d) HOLD e)SID and SOD
READY : It is used by the microprocessor to sense whether a peripheral is ready or not for data transfer. If not, the processor waits. It is thus used to synchronize slower peripherals to the microprocessor.
ALE : In 8085 , ADo to AD7 lines are multiplexed and lower half of address (Ao to A7) is available only during T1 of the machine cycle. The latching of lower half address from themultiplexed address lines byusing ALE signal.
IO/M - indicates whether I/O operation or memory operation is being carried out.
HOLD : This signal indicates that another master is requesting for the use of address bus, data bus and control bus.
SID(Serial Input Data) : This input signal is used to accept serial data bit by bit from the external device.
SOD(Serial Output Data) : This is an output signal which enables the transmission of serial data bit bybit to the external device.
Comparison between full address decoding and partial address decoding ?
Full Address Decoding
All higher address lines are decoded to select the memory or I/O device.
More hardware is required to design decoding logic.
Higher cost for decoding circuit.
No Multiple addresses.
Used in large systems
Partial Address decoding
Few higher address lines are decoded to select the memory or I/O device.
Hardware required to design decoding logic is less and sometimes it can be eliminated.
Less cost for decoding circuit.
It has a advantage of multiple addresses.
Used in small systems
What is ALE ?
The ALE (Address latch enable) is a signal used to demultiplex the address and data lines using an external latch. It is used to enable the external latch.