READ-ONLY MEMORY

Most computer systems necessitate memories that contain permanently stored or rarely altered data. A prime example of this would be math tables and permanent program data. Storage of this type of memory unit is provided with read-only memory. Information is often placed in this type of memory unit when the chip is manufactured. ROM data is non-volatile, which means that it is not lost when the power source is removed or turned off.

Read0only memory is achieved in a variety of ways. One process employs fusible links built into each memory cell. A data pattern can then be placed into memory by “blowing out” the unwanted fusible links. This action may be used to open interconnecting conductors, place a diode between two connections, or place a small capacitor between two electrodes. A fusible link cannot be reformed after it has been destroyed. The fusible link principle is used only once to program a read-only memory chip.

Erasable programmable read-only memory (EPROM) can be optically erased by exposure to an ultraviolet light source. After light exposure each cell of the entire unit goes to a zero state. Writing data into the chip again initiate the new program.

Erasing the charged data of each MOS cell is achieved by exposing the chip to ultraviolet light. This action temporarily makes the silicon-dioxide insulation layer more conductive. As a result, excessive leakage causes the floating gate charge to

dissipate. In practice, each cell of the chip is discharged by the exposure process at the same time. Memory can be restored by writing data back into each transistor cell. EPROMs of this type can be altered while in the circuit board if the need arises.

An alternative to EPROM is electrically erasable programmable read-only memory (EEPROM). This type of chip permits erasures of individual cells or word locations instead of the entire chip. Cell structure is similar to the EPROM, but the floating gate structure of each cell is altered by having a discrete interface insulation strip between it and the drain. Selective charge and discharge of each cell can be achieved by signals applied to the gate connection. The potential usefulness of EEPROM is quite large. It is presently used in programmable controllers, data loggers, and systems that have user-entered, alterable programs.

5. Find English equivalents of the following words and word combinations:

Ультрафиолетовый свет, взрыв, разнообразие, постоянно хранящийся, конденсатор, плавная связь, заряд, изоляционный слой, разрушать, изменять, электрически стираемый, программный контроллер, программа доступная для пользователя, зарядка и разрядка батареи.

6. Complete the sentences according to the content of the text:

1. The main example of ROM memory may be ………

2. Information is often placed in this type of memory unit when ………………

3. The fusible-link principle is used only once to ……………………….

4. Erasable programmable read-only memory can be erased by……………………

5. Memory cell can be restored by …………………………….

6. EEPROM is an alternative to ………………………………..

7.This type of chip permits ………………………………………

8. EEPROM is used in……………………………………………….

7. Speak on Read-Only Memory.

TEXT C

Поиск по сайту: