National MM5740 encoder serves as interface between keyboard and MM5204 4K PR0M capable of handling 90 four-mode keys. Encoder includes all Iogic needed for key validation, two-key or N-key rollover, bounce masking, mode selection, and strobe generation. Key code outputs can be defined by user. Bit-paired coding system of en coder has five common bits (B1-B4 and B9) and four variable bits (B5-B8) for each key. Each keyswitch is defined by one X drive line and one Y sense line of encoder ,Combination gives totalof 360 9-bit codes,－''Memory ApplicationsHandbook,'' National Semiconductor,SantaClara,CA,1978,p 5-⒌-5－8.
Required Field 
