摘要： Device Families:TTL (74xx) True TTL 74L Low power 74S Schottky 74H High speed74LS Low power - Schottky 74AS Advanced - Schottky 74ALS Advanced - Low power - Schottky 74F(AST) Fast - (Advanced - Schottky) 74C CMOS...................check Vcc levels 74HC (U) High speed - CMOS (Unbuffered output) 74HCT 阅读全文