Explanation on Read Only Memory

The following is the characteristic of Read Only Memory (ROM).
  • Non-volatile(data remain even the power cut off)
  • Mainly using in Embedded System
  • Only can write the information once at time of manufacture
  • Can only read the data but no write therefore call Read Only Memory
  • It is directly accessible.
  • Example of type:
    • Programmable ROM
    • Erasable Programmable ROM
    • Electrically Erasable Programmable ROM
  •  Cheaper than RAM
  • Read rate is slow than RAM
The logic value is 0 if the transistor is connected to ground like the picture above.

READ OPERATION

First ,the word line is activate to close the transistor .After the transistor is close,the voltage on the bit line drop near zero if there is a connection between the transistor and ground,else the bit line remain at high voltage which mean a logic value 1.

The sense circuit at the end of the bit line generates the proper output values.

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