EPROM Information
Last revised: October 29, 2024
Reviewed by: Scott Orlosky, consulting engineer
Image Credit: Allied Electronics, Inc. | Digi-Key Corporation
Erasable programmable read-only memory (EPROM) chips are programmable, reusable computer chips that can be erased using ultraviolet light and reprogrammed with a PROM programmer or PROM “burner”. Programming or burning an EPROM chip injects electrons with an elevated voltage into the floating gate a field-effect transistor, trapping the electrons and forcing a reading of zero. Erasing an EPROM chip bombards the chip with ultraviolet radiation through a quartz window to provide the trapped electrons with enough energy to escape the floating gate. To prevent slow erasure over a period of years from sunlight and fluorescent lights, the quartz window is covered with an opaque label during normal use.
EPROM Applications
EPROMs are used widely in personal computers because it enables manufacturers to change the contents of programmable read-only memory before the computer is shipped. Since EPROM chips do not require power to retain their data, they are commonly used to store BIOS information (Basic Input/Output System) and basic software for modems, video cards, and other peripherals. Flash EPROM or FEPROM incorporates FLASH technology and is available from some chip manufacturers. Other architectural considerations include density, which is the capacity of the memory chip expressed in bits, as well as the number of rows and columns. With EPROM, each row stores a memory word and connects to a word line for addressing purposes. The number of columns equals the bits per word. Each column connects to a sense / write circuit.
Selection Criteria
Selecting EPROM chips requires the selection of a serial or parallel data bus and the analysis of several performance specifications.
- Operating current is the minimum current needed for active chip operation.
- Standby current is the minimum current needed during inactivity.
- Power dissipation, which is generally expressed in watts or milliwatts, is the total power consumption of the device.
- Measured in nanoseconds (ns), access time indicates the speed of memory and represents a cycle that begins when the CPU sends a request to memory and ends when the CPU receives the data requested.
- Some EPROM chips support a specific temperature range and feature mechanical and electrical specifications that are suitable for commercial or industrial applications.
- Other EPROM chips meet screening levels for military specifications (MIL-SPEC).
- EPROM chips vary in terms of supply voltage, logic family, and package type.
- Common logic families include standard, fast, high-speed and advanced CMOS; emitter coupled logic (ECL); TTL and Fairchild advanced Schottky TTL (FAST); gunning technology; and crossbar switch technology (CBT).
- Common package types include ball grid array (BGA), quad flat package (QFP), single in-line package (SIP), and dual in-line package (DIP). Many packaging variants are available for EPROM chips.
- Common packaging materials include plastic, ceramic, metal, and glass.
Standards
EPROM FAQs
How do EPROMs differ from other types of programmable memory?
Reusability
EPROM: Unlike PROM (Programmable Read-Only Memory), which can only be programmed once, EPROMs can be erased and reprogrammed. This is achieved by exposing the memory chip to ultraviolet (UV) light, which erases the stored data, allowing the chip to be reprogrammed.
EEPROM: Electrically Erasable Programmable Read-Only Memory (EEPROM) can also be erased and reprogrammed, but it uses electrical signals instead of UV light, making it more convenient for frequent updates.
Erasure Method
EPROM: Requires exposure to UV light for erasure, which is a somewhat inconvenient process as it requires the chip to be removed from its circuit.
EEPROM: Can be erased electrically, allowing for in-circuit reprogramming without the need for removal.
Data Retention
EPROM: Non-volatile, meaning it retains data without power, making it suitable for storing firmware and BIOS information in computers.
EEPROM: Also non-volatile, but allows for more flexible data storage and updates due to its electrical erasure capability.
Applications
EPROM: Commonly used in applications where the data does not need to be changed frequently, such as in microcontroller programming and storing BIOS information.
EEPROM: Used for applications requiring frequent updates, such as small data storage in embedded systems.
What is the process of erasing and reprogramming an EPROM?
The process of erasing and reprogramming an EPROM involves several steps, primarily requiring the use of ultraviolet (UV) light for erasure.
Erasure Process
Exposure to UV Light: EPROM chips have an optical window on them, which allows UV light to penetrate and erase the stored data. The chip must be removed from its circuit and placed under a UV light source. The UV source wavelength is typically 253.7 nm. The energy level is 4000uW/sq cm at a distance of 2.5 cm. This will typically cause complete erasure within 20 to 30 minutes. Caution must be used with this UV wavelength. It is within the range of UVC which is the most dangerous for even fairly short exposure. Such exposure can cause sunburn, skin cancers and eye damage.
Complete Erasure: This exposure to UV light erases the memory by resetting the charge on the floating gate transistors within the chip. The entire memory of the EPROM must be erased before any new data can be written. This is because the UV light affects the entire chip uniformly, and partial erasure is not possible.
Reprogramming Process
Programming: After erasure, the EPROM can be reprogrammed with new data. This is typically done using a special device called a programmer, or burner which writes the new data to the chip by applying electrical signals to the appropriate memory cells.
Verification: Once the programming is complete, the data is usually verified to ensure that it has been written correctly. This involves reading back the data from the EPROM and comparing it to the intended data.
This method of erasure and reprogramming is inconvenient compared to EEPROM, which can be erased and reprogrammed electrically without removal from the circuit.
What are the advantages and disadvantages of using EPROM compared to EEPROM?
Advantages of EPROM
Non-volatility: EPROM retains data without power, making it suitable for storing firmware and BIOS information in computers.
Disadvantages of EPROM
Erasure Method: EPROM requires exposure to ultraviolet (UV) light for erasure, which is inconvenient as it necessitates removing the chip from its circuit.
Complete Erasure: The entire memory must be erased before reprogramming, as partial erasure is not possible.
Advantages of EEPROM
Convenient Erasure: EEPROM can be erased electrically, allowing for in-circuit reprogramming without removal, which is more convenient than the UV light method used for EPROM.
Flexibility: EEPROM allows for more flexible data storage and updates due to its electrical erasure capability.
Disadvantages of EEPROM
Complexity: The electrical erasure process typically requires a voltage higher than normal operation, which can add complexity to the design.
How does the UV light erasure method work in detail?
EPROM chips are designed with an optical window that allows ultraviolet (UV) light to penetrate the chip. This window provides a path for the UV light to reach the memory cells.
To erase the data stored in an EPROM, the chip must be removed from its circuit and exposed to a UV light source. The UV light resets the charge on the floating gate transistors within the chip, effectively erasing the stored data.
The specifics of wavelength, proximity of the UV source to the window, and the intensity and duration of exposure must be followed to ensure full erasure.
The UV light affects the entire chip uniformly, meaning that the entire memory must be erased before any new data can be written. Partial erasure is not possible with this method.
After erasure, the EPROM can be reprogrammed with new data. This is typically done using a special device called a programmer, which writes the new data to the chip by applying electrical signals to the appropriate memory cells.
Once the programming is complete, the data is usually verified to ensure that it has been written correctly. This involves reading back the data from the EPROM and comparing it to the intended data.