27C256 256K CMOS EPROM — 150ns Datasheet

The 150ns rating specifies the maximum access time — the delay between asserting a valid address and receiving valid data at the output pins. A 150ns 27C256 is suitable for systems with bus speeds up to approximately 6 MHz without wait states. Faster grades (70ns, 90ns, 120ns) exist for higher-speed microprocessor designs.

Multiple manufacturers produce pin-compatible 27C256 EPROMs, including AMD (Am27C256), Hitachi (HN27C256), Fujitsu (MBM27C256), NEC (uPD27C256), SGS-Thomson (M27C256), Seeq Technology, and WaferScale Integration. All are electrically and pin-compatible, allowing cross-sourcing without board redesign, which is critical for legacy system maintenance and second-sourcing strategies.

The 27C256 is erased by exposing its die through the quartz window to UV light at 253.7nm wavelength for typically 15–20 minutes using a UV eraser. Once fully erased (all bits read as FFh), the device is reprogrammed using a compatible EPROM programmer applying specified programming voltages and pulse widths per the manufacturer's datasheet.

The 27C256 is widely used for embedded firmware and boot-code storage, BIOS in legacy PC systems, industrial control program memory, lookup tables, and configuration data storage. It is also employed in military and defense electronics, telecommunications equipment, prototype development, and as a replacement in legacy systems requiring nonvolatile reprogrammable memory.

Yes. Military-specification (Mil-spec) 27C256 variants are available from multiple manufacturers including AMD and NEC. These devices meet MIL-STD screening requirements for extended temperature ranges, enhanced reliability testing, and controlled handling. LEVEL SOLUTIONS stocks both commercial and Mil-spec package types across all supported manufacturers and can supply to defense contractor requirements.

27C256 EPROMs are electrostatic-sensitive devices requiring ESD-compliant handling throughout storage, shipping, and assembly. LEVEL SOLUTIONS stores all EPROM inventory in an ESD-compliant warehouse using anti-static bags, trays, and controlled environments. Additionally, stored devices should be protected from ambient UV light sources to prevent inadvertent erasure of programmed data.