The Atmel AT27C520 EPROM, with its 64K Bytes of storage, combined with a novel multiplexed address/data scheme and an internal latch pin, make it the ideal External Program Memory storage solution for the Atmel AT89XXX Micro- Controller family. A simple scheme can be constructed where the AT89XXX P0 port serves as both the lower order address byte (to the EPROM) as well as the data bus (from the EPROM), while the P2 port serves as the high order address byte (to the EPROM). Additionally, the AT27C520 can be accessed in less than 90 nS. max. eliminating wasteful wait states. Figure 1 shows the necessary block diagram. Table 1 contains the necessary interface connections.