Introduction to Programmable IC Memory Types

Memory technology has no effect on the logical operation of a device. Due to the different processing steps required, some electrical characteristics (EC) may vary between devices with the same feature set/pinout but with different memory technologies. An example is that the VIL (Input Low Voltage) may have some difference between typical EPROM devices. Also, each device has a variety of frequency ranges and packaging options depending on the application and production requirements. When discussing the functionality of the device, the memory technology and the voltage range do not matter. The main programmable memory types are PROM, EPROM, EEPROM, ROM, and Flash type memory. NAND, eMMC and UFS devices are used where high memory density is needed.

  • What is a ROM?
ROM stands for read only memory. ROM is also called a masked ROM since they are already programmed at the manufacture line for cost efficiency. On the other hand, a bug in the software may cause ROMs to become worthless. Beware that some masked ROMs are unreadable by EPROM programmers.
  • What is the difference between ROM and RAM?
Both RAM and ROM provide the user random access to stored data. However, RAM provides only short term memory since data stored in RAM is lost when power is turned off. ROM, on the other hand, provides long-term storage since data is permanently etched into the ROM chip. Other difference between the two is that RAM's data can frequently and speedily be altered and changed at will. ROM can't be reconfigured at all.
  • What is a PROM?
PROMs (Programmable Read Only Memory) consist of an array of fuses and are programmed one-time. Programming is accomplished with a current instead of a voltage as EPROMS.
  • What is an EPROM?
EPROM (Erasable Programmable Read Only Memory) can be programmed and erased enabling them to be re-used. Erasure is accomplished using an UV (Ultra Violet) light source that shines through a quartz erasing window in the EPROM package. To learn more about EPROM programming, please refer here.
  • What is OTP?
OTP ( One Time Programmable) EPROMs are identical to an erasable EPROM, but lack an erasing window to reduce costs. To reduce the cost these EPROMs come in a windowless plastic carrier, which is cheaper than the costly ceramic package required for the erasing window. They can be programmed one time only, so these are used after the code is bug-free.
  • What is EEPROM Devices
An EEPROM ( Electrically Erasable Programmable Read Only Memory) is similar to an EPROM but the erasure is accomplished using an electric field instead of an UV light source. This eliminates the need of a window. Usually, EEPROM refers to a device that requires a programmer or special voltage to program. The lower cost plastic packages can be used for these devices. To learn more about EEPROM programming, please refer here.
  • What is a Flash?
A flash is a nonvolatile memory, which is similar to an EEPROM. But, the flash are erased all at once, whereas common EEPROMs can erase one byte at a time. In circuit writing and erasing is possible because no special voltages are required. In order to accomplish in-circuit operation, it requires special application software routines. To learn more about Flash programming, please refer here.
  • What is a NAND Flash?
NAND flash memories are used to reduce cost per bit and increase chip capacity so that flash memory technology can compete with older hard disk technology. NAND flash memory devices are permitted to contain certain number of faults (bad blocks) thus bad block handling methods are very important when dealing with NAND flash devices. To learn more about NAND flash programming, please refer here.
  • What is a NOR Flash?
NOR flash are preferred devices to store code in small capacities. NOR flash offers fast reading but slow writing and erasing compared to NAND flash devices. NOR flash offer random access compared to serial access of NAND flash devices. To learn more about NOR Flash programming, please refer here.
  • What is an eMMC?
eMMC devices (embedded Multi Media Controller) are used in most cell phones, tablets and laptops. These chips have both flash memory and flash memory controller implemented on the same silicon die. eMMC hides the complexities of NAND flash memory technology and reduces time and development efforts. To learn more about eMMC programming, please refer here.

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