M27C800 is an 8 Mbit EPROM offered in the two ranges UV (ultra violet erase) and OTP (one time programmable). It is ideally suited for micro-processor systems requiring large data or program storage. It is organised as either 1 Mwords of 8 bit or 512 Kwords of 16 bit. The pin-out is compatible with the most common 8 Mbit Mask ROM. The FDIP42W (window ceramic frit-seal package) has a transparent lid which allows the user to ex- pose the chip to ultraviolet light to erase the bit pat- tern. A new pattern can then be written rapidly to the de- vice by following the programming procedure. For applications where the content is programmed only one time and erasure is not required, the M27C800 is offered in PDIP42, PLCC44 and SO44 packages.