Active EPROM for firmware storage
The CY27H256-35ZC is an Infineon 256Kbit EPROM organized as 32K x 8, with a 35 ns access time and a parallel interface. The 35 ns access time means the memory can deliver data within 35 ns of the address being stable — fast enough for most 8-bit microcontroller and DSP buses running at clock rates up to about 28 MHz without wait states. The parallel interface simplifies glue logic; the EPROM's non-volatile nature holds firmware through power cycles.
Lifecycle and supply posture
For BOM planning, this EPROM is a single-source component — there is no official pin-compatible second source from Infineon or another manufacturer. The closest functional alternative in the non-volatile parallel 256Kbit space is the FM28V020-SG (FRAM, 140 ns access, 2.0 V supply, -40°C to 85°C), but its slower access time and different supply voltage mean a board redesign is required.
Housed in a 28-TSOP surface-mount package, the CY27H256-35ZC is supplied in bulk (tube) quantity. The 0.50 mm pitch TSOP footprint is standard for 256Kbit EPROMs of this generation; verify the pinout against your PCB layout — the 28-pin TSOP pin 1 orientation is marked by a notch on the package body. The commercial temperature range (0°C to 70°C) limits deployment to indoor, temperature-controlled environments.