Memory Devices – IQ – 1

1. List basic types of programmable logic devices ?
(1) Read only memory 
(2) Programmable logic Array 
(3) Programmable Array Logic 

2. Explain ROM ?
A read only memory(ROM) is a device that includes both the decoder and the OR gates within a single IC package. It consists of n input lines and m output lines. Each bit combination of the input variables is called an address. Each bit combination that comes out of the output lines is called a word. The number ofdistinct addresses possible with n input variables is 2n

3. Define address and word for ROM ?
 In a ROM, each bit combination of the input variable is called on address. Each bit combination that comes out of the output lines is called a word. 

4. State the types of ROM ?
(1) Masked ROM. 
(2) Programmable Read only Memory.
(3) Erasable Programmable Read only memory. 
(4) Electrically Erasable Programmable Read only Memory. 

5. Explain PROM ?
PROM (Programmable Read Only Memory) 
It allows user to store data or program. PROMs use the fuses with material like nichrome and polycrystalline. The user can blow these fuses by passing around 20 to 50 mA of current for the period 5 to 20µs. The blowing of fuses is called programming of ROM. The PROMs are one time programmable. Once programmed, the information is stored permanent. 

6. Explain EPROM ?
EPROM(Erasable Programmable Read Only Memory) 
EPROM use MOS circuitry. They store 1’s and 0’s as a packet of charge in a buried layer of the IC chip. We can erase the stored data in the EPROMs by exposing the chip to ultraviolet light via its quartz  window for 15 to 20 minutes.  It is not possible to erase selective information. The chip can be reprogrammed. 

7. Explain EEPROM ?
EEPROM(Electrically Erasable Programmable Read OnlyMemory) 
EEPROM also use MOS circuitry. Data is stored as charge or no charge on an insulated layer or an insulated floating gate in the device. EEPROM allows selective erasing at the register level rather than erasing all the  information since the information can be changed by using electrical signals. 

8. Define PROM ?
PROM is Programmable Read Only Memory. It consistsof a set of fixed AND gates connected to a decoder and a programmable OR array.

9. What is RAM ? 
Random Access Memory. Read and write operations can be carried out. 

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