The 74HC/HCT595 are high-speed Si-gate CMOS devices

　　and are pin compatible with low power Schottky TTL

　?。↙STTL）。 They are specified in compliance with JEDEC

　　standard no. 7A.

　　The “595” is an 8-stage serial shift register with a storage

　　register and 3-state outputs. The shift register and storage

　　register have separate clocks.

　　Data is shifted on the positive-going transitions of the

　　SHCP input. The data in each register is transferred to the

　　storage register on a positive-going transition of the STCP

　　input. If both clocks are connected together， the shift

　　register will always be one clock pulse ahead of the

　　storage register.

　　The shift register has a serial input （DS） and a serial

　　standard output （Q7’） for cascading. It is also provided with

　　asynchronous reset （active LOW） for all 8 shift register

　　stages. The storage register has 8 parallel 3-state bus

　　driver outputs. Data in the storage register appears at the

　　output whenever the output enable input （OE） is LOW.