Electronic Components

The 74HC20; 74HCT20 is a dual 4-input NAND gate. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of VCC. 

74HC221 is a 16 Pin Hex D-type Flip-Flop with Reset IC having 2V to 6V Operating Voltage range with 5.2mA output current and 1uA low input current. It utilize  advanced  silicon-gate  CMOS  technology. They feature speeds comparable to low power Schottky  TTL  circuitry  while  retaining  the  low  power  and  high noise immunity characteristic of CMOS circuits. Each multivibrator features both a negative, A, and a positive,  B,  transition  triggered  input,  either  of  which  can  be used as an inhibit input. Also included is a clear input that when  taken  low  resets  the  one  shot.  The  74HC221 can be triggered on the positive transition of the clear while A is held LOW and B is held HIGH.

The 74HC221A high speed monostable multivibrators (one shots) utilize advanced silicon-gate CMOS technology. They feature speeds comparable to low power Schottky TTL circuitry while retaining the low power and high noise immunity characteristic of CMOS circuits. Each multivibrator features both a negative, A, and a positive, B, transition triggered input, either of which can be used as an inhibit input. Also included is a clear input that when taken low resets the one shot. The 74HC221A can be triggered on the positive transition of the clear while A is held LOW and B is held HIGH. The 74HC221A is a non-retriggerable, and therefore cannot be retriggered until the output pulse times out. Pulse width stability over a wide range of temperature and supply is achieved using linear CMOS techniques. The output pulse equation is simply: PW = (REXT) (CEXT); where PW is in seconds, R is in ohms, and C is in farads. All inputs are protected from damage due to static discharge by diodes to VCC and ground. 

The 74HC237 is a 3-to-8 line decoder, demultiplexer with latches at the three address inputs (An). The 74HC237 essentially combines the 3-to-8 decoder function with a 3-bit storage latch. When the latch is enabled (LE = LOW), the 74HC237 acts as a 3-to-8 active LOW decoder. When the latch enable (LE) goes from LOW-to-HIGH, the last data present at the inputs before this transition, is stored in the latches. Further address changes are ignored as long as LE remains HIGH. The output enable input (E1 and E2) controls the state of the outputs independent of the address inputs or latch operation. All outputs are HIGH unless E1 is LOW and E2 is HIGH. The 74HC237 is ideally suited for implementing non-overlapping decoders in 3-state systems and strobes (stored address) applications in bus-oriented systems.

The 74HC244; 74HCT244 is an 8-bit buffer/line driver with 3-state outputs. The device 

74HC253 Dual 4-Bit Multiplexer IC (74253 IC) DIP-16 Package

The 74HC253 are high-speed Si-gate CMOS device sand are pin compatible with low power Schottky TTL(LSTTL). They are specified in compliance with JEDEC standard no. 7A. The 74HC253 have two identical 4-input multiplexer switch 3-state outputs which select two bits from four sources selected by common data select inputs (S0,S1).When the individual output enable (1OE, 2OE) inputs of the 4-input multiplexers are HIGH, the outputs are forced to the high impedance OFF-state. The ?253? is the logic implementation of a 2-pole, 4-position switch, where the position of the switch is determined by the logic levels applied to S0and S1.