A Read-Only Memory (ROM) chip can be found in computers and indeed most electronic items. The chip is programmed with specific data and is typically integrated within your device. The data stored within a ROM is often referred to as “non-volatile”. This simply means that when the power is removed the data stored within the chip is not lost and remains intact for the next time you use your electronic gadget. They are also unchangeable unless you use a specific and complicated operation to change the data.
A ROM chip contains an intersection of columns and rows and uses a diode to connect all these lines together. The diode allows electrical current to flow in a certain direction, but is controlled by the “forward break-over” which will determine exactly how much current the diode should hold before it passes it on. A ROM chip will require the perfect and clear data to be programmed into it when the chip is created. However if it is programmed incorrectly or if the chip needs to be updated, it is pretty much rendered useless and may as well be thrown away.
In order to create a ROM chip you face a seriously arduous task, however the benefits of this form of technology completely outweigh anyway drawbacks you may face. A ROM chip, once created, will cost very little money, is extremely reliable and will use very little electrical power. The majority of electrical devices have been programmed to control a ROM chip and therefore they should cause you very few problems, if any. There are several types of ROM and these include:-
PROM – If we had to create and produce ROM chips from scratch, not only does this take a lot of time, it can also cost a pretty penny. This is why developers have created PROM or Programmable Read-Only Memory. By using a programmer you can purchase a PROM and code this to do what you want yourself. The structure of a PROM is very similar to an ordinary ROM in that it has intersections of rows and columns however each and every intersection has a fuse connecting them together. Should you send a charge through a column, this will pass through a fuse straight onto a row. You should be aware though that the higher amount of voltage you use, the more likely you are to burn out the fuse or to give its technical name “burning the PROM”.
EPROM – An EPROM is an Erasable Programmable Read-Only Memory and can save you a lot of money. Should you merely use ROMs and Proms, you may find that this can become fairly expensive. An EPROM will provide voltage at a specific level which is very much dependent on the type of EPROM you use. An EPROM will once again have a grid with intersections of rows and columns, however this time each intersection is connected by two transistors. A thin layer of oxide will separate the two transistors, which are commonly known as the control gate and the floating gate. An electrical charge will be applied to the floating gate and will eventually drain to the ground. This is known as tunnelling and will actually alter where electrons are placed within the floating gate. The electrons will be pushed through the thin oxide layer and become trapped on the other side which causes a negative charge, which literally acts as a barrier between the two gates. Should you ever need to rewrite an EPROM you will have to erase it first. You must break through the electrons with a strong enough level of energy to make this happen. The easiest way to achieve this is to place the EPROM under a UV light for several minutes.
EEPROM and Flash Memory – An Electrically Erasable Read-Only Memory (EEPROM) can be considered your next step up from an EPROM. In order to rewrite the chip it does not need to be removed from the device, you do not have to completely erase everything from the chip and are able to remove a specific portion of memory and you do not actually require any additional equipment to perform this task. EEPROMs are extremely versatile, but you must also consider that they are very slow. In fact they are far too slow to use in the majority of products as it will not allow you to make any quick changes to the data contained in the chip that may be required. This is the reason for Flash Memory. Flash Memory will work a lot faster than a traditional EEPROM and will apply an electrical field to the entire chip.