View tc74hc166p datasheet:

TC74HC166P IL00D C-MOS 8-BIT SHIFT REGISTER —TOP VIEW— 1 DS VDD DS IN 1 16 2 P1 3 P2 P1 IN 2 15 S/P IN 4 P3 5 13 P4 Q8 P2 IN 3 14 P8 IN 10 P5 11 P6 P3 IN 4 13 Q8 OUT 12 P7 14 P8 P4 IN 5 12 P7 IN 6 7 CKA IN 6 11 P6 IN S/P RD (CLOCK) 15 9 CKB IN 7 10 P5 IN (CLOCK) DS ; DATA SERIAL INPUT P1 - P8 ; DATA PARALLEL INPUT 8 GND 9 RD IN CK ; CLOCK (RESET) P1 P2 P3 P7 P8 2 3 4 12 14 15 S/P 13 D D D D D Q Q8 1 DS Q Q Q Q RD RD RD RD RD 6 CKA 7 CKB 9 RD CKA CKB CK INPUT OUTPUT 0 0 0 RD S/P CK DS P1-P8 Q8 X 1 1 0 X X X X 0 1 X 1 1 X 0 X X Q8o 1 1 1 0 X 1-8 8 1 1 1 1 1 X Q7n 0 ; LOW LEVEL 0 1 1 0 X Q7n 1 ; HIGH LEVEL 0 1 X X X A8o X ; DON’T CARE