What is EPROM?
EPROM stands for erasable programmable read only memory and is a type of solid state memory chip that retains its memory contents without the help of a power supply.
The basic transistor device in an EPROM is different from the normal MOS transistor. A floating gate avalanche injection MOS transistor is used. There are two gates to this MOS transistor. One is a floating gate, meaning that it has no electrical connection to that gate.
Types of solid state memory available with different desirable characteristics:
Read Only Memory, non-volatile (memory contents are retained even without the help of a power supply), are low power and high density.
Random Access Memory is volatile.
Programmable ROM allows you to write your own content or program. It cannot be erased so you can only program it once.
You can erase whatever you have programmed and can reprogram it thus allowing it to be reused. It can be erased with ultra violet (UV) light which basically means that you have to take the chip out from the circuit and expose the memory chip to UV lights. These memory chips come with a particular package which enables this to happen. Standard room lighting cannot be used to erase the chip as it does not have enough UV light, however bright sunlight can cause erasure therefore this is why the window is protected with a label. There is a glass window on top which you can expose these memory cells to UV light. Once this happens the electrons which are in the floating gate, get excited because of the high energy they acquire and they overcome the silicon dioxide barrier and move over to the silicon substrate or the control gate and once they do this you are reducing the threshold voltage. This can take up to 30 minutes in which you have to expose it to UV light, after which the electrons move out from the floating gate and then it is ready for reprogramming.
Disadvantages of EPROM is that it takes time to erase the entire content. You don’t have control over which bits you want erased.
Differences between EPROM and EEPROM
EEPROM (electrically erasable programmable ROM) can be erased electrically and can be reprogrammed. The device it uses is called FLOTOX (Floating Gate Tunnelling Oxide) MOS. It is more flexible than EPROM, for example you can erase a single bit of memory internally at a time without removing the chip. There are also two transistors per cell instead of one so the density of an EEPROM is slightly less compared to the normal EPROM.

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Description Price Memory Size Organisation Interface Type Maximum Random Access Time Programming Voltage Reprogramming Technique In System Programmability Mounting Type Package Type Pin Count Dimensions Height Length Maximum Operating Supply Voltage
RS Stock No. 127-6545
Mfr. Part No.AT27C040-70JU
Each (In a Pack of 2)
4Mbit 512K x 8 bit - 70ns - OTP - Through Hole PLCC 32 14.04 x 11.5 x 3.17mm 3.17mm 14.04mm -
RS Stock No. 127-4047
Mfr. Part No.AT27C010-45JU
Each (In a Pack of 5)
1Mbit 128K x 8 bit - 45ns - OTP - Through Hole PLCC 32 14.04 x 11.5 x 3.17mm 3.17mm 14.04mm -
RS Stock No. 169-8318
Mfr. Part No.DS2502+
Each (In a Tube of 10)
1kbit - - - - - - Through Hole TO-92 3 4.95 (Dia.) x 3.94mm 3.94mm - -
RS Stock No. 127-6547
Mfr. Part No.AT27C040-90JU
Each (In a Pack of 2)
4Mbit 512K x 8 bit - 90ns - OTP - Through Hole PLCC 32 14.04 x 11.5 x 3.17mm 3.17mm 14.04mm -
RS Stock No. 177-1447
Mfr. Part No.AT27C2048-55JU
Each (In a Tube of 27)
2Mbit 128K x 16 bit Parallel 55ns - OTP - Surface Mount PLCC 44 16.66 x 16.66 x 4.06mm 4.06mm 16.66mm 5 V
RS Stock No. 540-4845
Mfr. Part No.DS2505+
16kbit - - - - - - Through Hole TO-92 3 - 4.95mm - -
RS Stock No. 178-4839
Mfr. Part No.AT27C020-55PU
Each (In a Tube of 12)
2Mbit 256K x 8 bit - 55ns - OTP - Through Hole PDIP 32 42.29 x 13.97 x 4.44mm 4.44mm 42.29mm -
RS Stock No. 137-519
Mfr. Part No.DS1982-F3+
1kbit - - - - - - - F3 MicroCan 2 17.36 (Dia.) x 3.1mm 3.1mm - -
RS Stock No. 127-6556
Mfr. Part No.AT27C256R-45JU
Each (In a Pack of 5)
256kbit 32K x 8 bit - 45ns - OTP - Through Hole PLCC 32 14.04 x 11.5 x 3.17mm 3.17mm 14.04mm -
RS Stock No. 127-6566
Mfr. Part No.AT27C512R-70PU
Each (In a Pack of 5)
512kbit 64K x 8 bit - 70ns - OTP - Through Hole PDIP 28 37.33 x 13.97 x 4.44mm 4.44mm 37.33mm -