Many old devices use socketed EPROMs for ROM and BIOS chips. Erasing these can be annoying and time consuming as they require a 20-30 minute UV erase cycle.
Replacing these chips with EEPROMs or Flash memory provides a convenient way to experiment with ROM and BIOS changes via reduced programming times. Fortunately, in many cases, equivalent parts exist and can still be sourced as New Old Stock or Used devices through parts brokers, Amazon, eBay, and Aliexpress.
27C Series
The 27C series of Parallel EPROMs use 5v (TTL). In many cases a larger memory part can replace a lower memory part by repeating the ROM. While some address lines will potentially float, this ensures they will always resolve to the same memory.
Access speed matters — in some cases replacing an EPROM with a slower EEPROM will cause issues. This is not always the case — sometimes manufactures used faster chips than were required in the circuit. If you want to use caution, always replace an EPROM with an EEPROM or Flash memory with faster (lower) access times than the chip you are replacing.
These ROMs correspond to the JEDEC pinout standards – generally replacements that follow this standard are compatible.
27C040
- Packages: DIP32, PLCC32
- Size: 4096kbits (512k * 8) = 512KiB
DIP32 Pinout
┌─────◡─────┐ Vpp │ ●1 32 │ Vcc A16 │ 2 31 │ A18 A15 │ 3 30 │ A17 A12 │ 4 29 │ A14 A7 │ 5 28 │ A13 A6 │ 6 27 │ A8 A5 │ 7 26 │ A9 A4 │ 8 25 │ A11 A3 │ 9 24 │ OE A2 │ 10 23 │ A10 A1 │ 11 22 │ CE A0 │ 12 21 │ O7 O0 │ 13 20 │ O6 O1 │ 14 19 │ O5 O2 │ 15 18 │ O4 GND │ 16 17 │ O3 └───────────┘
Original Parts
- AMD Am27C040
- Atmel/Microchip AT27C040
- Philips/Signetics/ST/NXP 27C040
- Texas Instruments TMS27C040
Replacement Parts
- Winbond W27E040
- Type: EEPROM
- Speeds: 90ns/120ns
- Compatible Packages: DIP32, PLCC32
27C020
- Packages: DIP32, PLCC32
- Size: 2048kbits (256k * 8) = 256KiB
DIP32 Pinout
┌─────◡─────┐ Vpp │ ●1 32 │ Vcc A16 │ 2 31 │ PGM A15 │ 3 30 │ A17 A12 │ 4 29 │ A14 A7 │ 5 28 │ A13 A6 │ 6 27 │ A8 A5 │ 7 26 │ A9 A4 │ 8 25 │ A11 A3 │ 9 24 │ OE A2 │ 10 23 │ A10 A1 │ 11 22 │ CE A0 │ 12 21 │ O7 O0 │ 13 20 │ O6 O1 │ 14 19 │ O5 O2 │ 15 18 │ O4 GND │ 16 17 │ O3 └───────────┘
Original Parts
- AMD Am27C020
- Atmel/Microchip AT27C020
- Holtek HT27C020
- Texas Instruments TMS27C020
Replacement Parts
- Greenliant GLS27SF020
- Type: Flash
- Speeds: 70ns
- Compatible Packages: DIP32, PLCC32
- Microchip SST39SF020
- Type: Flash
- Speeds: 55ns/70ns
- Note: Drop in replacement for read-only applications. For writing, pin 1 should be NC unlike the original 27C020.
- Compatible Packages: DIP32, PLCC32
- SST SST27SF020
- Type: Flash
- Speeds: 70ns
- Compatible Packages: DIP32, PLCC32
- Winbond W27C020
- Type: EEPROM
- Speeds: 70ns/90ns/120ns
- Compatible Packages: DIP32, PLCC32
27C010
- Packages: DIP32, PLCC32
- Size: 1024kbits (128k * 8) = 128KiB
DIP32 Pinout
┌─────◡─────┐ Vpp │ ●1 32 │ Vcc A16 │ 2 31 │ PGM A15 │ 3 30 │ NC A12 │ 4 29 │ A14 A7 │ 5 28 │ A13 A6 │ 6 27 │ A8 A5 │ 7 26 │ A9 A4 │ 8 25 │ A11 A3 │ 9 24 │ OE A2 │ 10 23 │ A10 A1 │ 11 22 │ CE A0 │ 12 21 │ O7 O0 │ 13 20 │ O6 O1 │ 14 19 │ O5 O2 │ 15 18 │ O4 GND │ 16 17 │ O3 └───────────┘
Original Parts
- Atmel/Microchip AT27C010
- Fairchild/National Semiconductor NM27C010
- Maxwell 27C010
Replacement Parts
- Greenliant GLS27SF010
- Type: Flash
- Speeds: 70ns
- Compatible Packages: DIP32, PLCC32
- Microchip SST39SF010
- Type: Flash
- Speeds: 55ns/70ns
- Note: Drop in replacement for read-only applications. For writing, pin 1 should be NC unlike the original 27C010.
- Compatible Packages: DIP32, PLCC32
- SST SST27SF010
- Type: Flash
- Speeds: 70ns
- Compatible Packages: DIP32, PLCC32
- Winbond W27C010
- Type: EEPROM
- Speeds: 70ns
- Compatible Packages: DIP32, PLCC32
27C512
- Packages: DIP28, PLCC32, TSOP28
- Size: 512kbits (64k * 8) = 64KiB
DIP28 Pinout
┌─────◡─────┐ A15 │ ●1 28 │ Vcc A12 │ 2 27 │ A14 A7 │ 3 26 │ A13 A6 │ 4 25 │ A8 A5 │ 5 24 │ A9 A4 │ 6 23 │ A11 A3 │ 7 22 │ OE/Vpp A2 │ 8 21 │ A10 A1 │ 9 20 │ CE A0 │ 10 19 │ O7 O0 │ 11 18 │ O6 O1 │ 12 17 │ O5 O2 │ 13 16 │ O4 GND │ 14 15 │ O3 └───────────┘
Original Parts
- Atmel/Microchip AT27C512
- Intel 27512
- Intel 27C512
- Macronix MX27C512
- Maxwell 27C512
- ST M27C512
Replacement Parts
- Greenliant GLS27SF512
- Type: Flash
- Speeds: 70ns
- Compatible Packages: DIP28, PLCC32
- SST SST27SF512
- Type: Flash
- Speeds: 70ns
- Compatible Packages: DIP28, PLCC32
- Winbond W27C512
- Type: EEPROM
- Speeds: 45ns/70ns/90ns/120ns
- Compatible Packages: DIP28, PLCC32
27C256
- Packages: DIP28, PLCC32, TSOP28
- Size: 256kbits (32k * 8) = 32KiB
DIP28 Pinout
┌─────◡─────┐ Vpp │ ●1 28 │ Vcc A12 │ 2 27 │ A14 A7 │ 3 26 │ A13 A6 │ 4 25 │ A8 A5 │ 5 24 │ A9 A4 │ 6 23 │ A11 A3 │ 7 22 │ OE A2 │ 8 21 │ A10 A1 │ 9 20 │ CE A0 │ 10 19 │ O7 O0 │ 11 18 │ O6 O1 │ 12 17 │ O5 O2 │ 13 16 │ O4 GND │ 14 15 │ O3 └───────────┘
Original Parts
- Atmel/Microchip AT27C256
- AMD Am27C256
- Fairchild FM27C256
- Fairchild/National Semiconductor NM27C256
- Intel 27256
- Intel 27C256
- Macronix MX27C256
- Philips/Signetics/NXP 27C256
- Cypress CY27C256
- ST M27C256
- ST WS57C256
- Maxwell 27C256
Replacement Parts
- Atmel/Microchip AT29C256
- Type: Flash
- Speeds: 70ns
- Compatible Packages: DIP28, PLCC32
- SST SST27SF256
- Type: Flash
- Speeds: 70/90ns
- Compatible Packages: DIP28, PLCC32
- Winbond W27E257
- Type: EEPROM
- Speeds: 100ns/120ns/150ns
- Compatible Packages: DIP28, PLCC32
27C128
- Packages: DIP28, PLCC32
- Size: 128kbits (16k * 8) = 16KiB
DIP28 Pinout
┌─────◡─────┐
Vpp │ ●1 28 │ Vcc
A12 │ 2 27 │ PGM
A7 │ 3 26 │ A13
A6 │ 4 25 │ A8
A5 │ 5 24 │ A9
A4 │ 6 23 │ A11
A3 │ 7 22 │ OE
A2 │ 8 21 │ A10
A1 │ 9 20 │ CE
A0 │ 10 19 │ O7
O0 │ 11 18 │ O6
O1 │ 12 17 │ O5
O2 │ 13 16 │ O4
GND │ 14 15 │ O3
└───────────┘
Original Parts
- AMD Am27C128
- Atmel AT27C128
- Fairchild/National Semiconductor NMC27CP128
- Intel 27128
- Intel 27C128
- Microchip 27C128
- ST M27C128
- TI TMS27C128
Replacement Parts
- None
27C64
- Packages: DIP28, PLCC32, TSOP28
- Size: 64kbits (8k * 8) = 8KiB
DIP28 Pinout
┌─────◡─────┐
Vpp │ ●1 28 │ Vcc
A12 │ 2 27 │ PGM
A7 │ 3 26 │ NC
A6 │ 4 25 │ A8
A5 │ 5 24 │ A9
A4 │ 6 23 │ A11
A3 │ 7 22 │ OE
A2 │ 8 21 │ A10
A1 │ 9 20 │ CE
A0 │ 10 19 │ O7
O0 │ 11 18 │ O6
O1 │ 12 17 │ O5
O2 │ 13 16 │ O4
GND │ 14 15 │ O3
└───────────┘
Original Parts
- Atmel/Microchip AT27C64
- Fairchild/National Semiconductor NMC27C64
- Intel 27C64
- Intel M27C64
- Intel 2764A
Replacement Parts
- Atmel/Microchip AT28C64
- Type: EEPROM
- Speeds: 120ns
- Compatible Packages: DIP28, PLCC32, TSOP28
- Catalyst/Onsemi CAT28C64
- Type: EEPROM
- Speeds: 90ns/120ns/150ns
- Compatible Packages: DIP28, PLCC32, TSOP28