EEPROM memory

[cammhifi]

Just a quickie
What is the difference between ordinary memory and eeprom memory? Are they in the same place or are they two different types of file?
Mac

[rshayes]

EEPROM is an abbreviation for Electrically Erasable Programmable Read Only Memory. It is not ordinary memory.<p>Ordinary memory stores information as either the state of a flip-flop (static) or as a small amount of charge on a capacitor (dynamic). Either method can change the information stored in a matter of nanoseconds. The information is lost when power is interrupted.<p>Most microprocessors have no provision for loading a program. It takes a program to load a program. This initial program is stored in a ROM (Read Only Memory). A ROM is a memory that is written once, usually by an external programmer, and then read by a microprocessor. The original ROMs were mask programmable, which meant that the program was placed in the memory during the chip manufacturing process by altering one of the metalization masks used for manufacturing. Changing one bit in a program required fabricating a different mask. This could be very expensive, since a different mask might cost thousands of dollars.<p>The next step was the PROM (Programmable Read Only Memory). Originally, these stored information by electrical connections on the chip that could be removed by a programmer. In effect, each bit was represented by a fuse which could be blown by the application of pulses from an external programmer.<p>Later PROMs stored the information by storing charge on the floating gate of a MOS transistor. The gate was a piece of metal that was entirely surrounded by layers of very low leakage dielectric. The time required for the charge to leak off is on the order of several decades. The charge generates an electric field, which can be sensed by the channel of a MOS transistor in close proximity to the floating gate. The dielectric is thin enough that it can be penetrated by electrons with about 20 volts or so of energy. Again, writing a bit required an external programmer and required a considerable amount of time, typically about 50 milliseconds.<p>This type of memory can be erased by exposing it to ultraviolet light. This gives the electrons on the floating gate sufficient energy to leave the gate and return to the substrate of the circuit. This requires that the chip package have a window (usually fused quartz) that can transmit ultraviolet light. The erasing process erases the entire chip at once, and takes several minutes. This type of part was called an EPROM (Erasable Progeammable Read Only Memory).<p>The EEPROM (Electrically Erasable Programmable Read Only Memory) is the same device with structures that can electronically both add and remove charge from the floating gate. This eliminates the need for an external programmer. Altering a bit may take several milliseconds, and can only be done a limited number of times (possibly 100,000 times or more, but still limited). Reading a bit takes a few nanoseconds, and can be done indefinitely, so it is still considered a read-only memory.<p>All of the read-only memories (ROM, PROM, and EEPROM) retain the stored data without needing external power. This is the basic difference between them and notmal memory.<p>[ October 03, 2005: Message edited by: stephen ]</p>

[cammhifi]

Hi
I'll read your info later but say in a PIC12F629, where should I write or store data in the eeprom what are the address numbers. I seem to be getting errors when I compile my code. Is there a fixed block of numbers I should be using?
Mac

[philba]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Mac:
Hi
I'll read your info later but say in a PIC12F629, where should I write or store data in the eeprom what are the address numbers. I seem to be getting errors when I compile my code. Is there a fixed block of numbers I should be using?
Mac<hr></blockquote><p>have you looked at the datasheet? I believe it has all the info you need. you don't access the pic eeprom as memory but through the eeprom interface which consists of an address register, data reg and control registers and a voodoo code sequence for writing. look in section 8, it even includes code.