Memory Options

RAM
Random Access Memory (RAM) is used for temporary storage of data and instructions. The CPU can write information into and read information from a RAM in a random order. RAM is volatile in that its contents are lost when power is removed.

ROM
Read Only Memory (ROM) is a permanent form of memory that is written to during manufacture. The CPU can read information from a ROM location, but cannot write information into it. ROM information is non-volatile in that it does not change when power is removed.

EEPROM and EPROM
Electrically Erasable Programmable Read Only Memory (EEPROM) and Erasable Programmable Read Only Memory (EPROM) are both types of ROM that can be programmed by the user. EPROM can be erased by exposing it to ultraviolet light, whereas EEPROM can be erased electrically (i.e., in the application). Once erased, EPROMs and EEPROMs may be reprogrammed with new instructions and data. EEPROM and EPROM information is non-volatile in that it does not change when power is removed.

OTP
One-time Programmable Read Only Memory (OTPROM) is an EPROM that does not have a window on top of the package, which means that the memory cannot be exposed to ultraviolet light and therefore cannot be erased and reprogrammed. OTPROM versions of most microcontrollers are available to support your development and production needs. OTP information is non-volatile in that it does not change when power is removed.

Personality EPROM (PEP) and Personality EEPROM (PEEP)
Mask ROM MCUs are typically lower in cost compared to OTP, EPROM, or EEPROM MCUs in high volume applications. OTP, EPROM, and EEPROM MCUs have the advantage of being able to customize each microcontroller whereas a mask ROM MCU must have the same code.

Personality EPROM (PEP) is a small block of EPROM organized serially that can be added to mask ROM MCUs. While more expensive than mask ROM parts, they are typically cheaper than all EPROM or OTP parts and retain the advantage of customization.

Personality EEPROM (PEEP) is identical in function to PEP except the EPROM is replaced by EEPROM.

Typical applications of PEP and PEEP include:

  • Storage of electronic I.D. (serial number)
  • RF security systems (remote car locks, home alarm, etc)
  • Configuration data
  • Increase reliability and lower cost by eliminating dip switches
  • Allow more user friendly set-up and use
  • Calibration data
  • Correct for system variation at manufacturing or in the field