4021 IC 8-Bit Parallel-Serial Shift Register
The CD4021BE functions as an 8-bit parallel-in serial-out (PISO) shift register, providing a simple and effective way to read multiple digital inputs using a minimal number of microcontroller pins. It reads 8 digital signals in parallel and shifts them out serially using a clock signal. This capability makes it ideal for expanding input capacity in digital systems.
The IC integrates a parallel input latch that captures the input state on a logic-high signal at the strobe (parallel load) pin. Once latched, the data shifts out on each rising edge of the clock pulse. Designers rely on this IC in key scanning, switch monitoring, and remote input reading in microcontroller-based applications.
Key Features
8-bit parallel-in, serial-out shift register
Serial data output (Q) and complementary output (Q̅)
Asynchronous master reset
Separate parallel load and shift operations
Wide operating voltage: 3V to 15V
High noise immunity and low power CMOS design
TTL-compatible outputs
DIP-16 through-hole package
Pin Configuration (DIP-16)
| Pin | Label | Description |
|---|---|---|
| 1 | D5 | Parallel Data Input Bit 5 |
| 2 | D4 | Parallel Data Input Bit 4 |
| 3 | D3 | Parallel Data Input Bit 3 |
| 4 | D2 | Parallel Data Input Bit 2 |
| 5 | D1 | Parallel Data Input Bit 1 |
| 6 | D0 | Parallel Data Input Bit 0 (LSB) |
| 7 | CLOCK | Serial Clock Input |
| 8 | GND | Ground ‘ |
| 9 | Q̅ | Complementary Serial Data Output |
| 10 | Q | Serial Data Output |
| 11 | STROBE | Parallel Load (Latch Inputs on High) |
| 12 | D6 | Parallel Data Input Bit 6 |
| 13 | D7 | Parallel Data Input Bit 7 (MSB) |
| 14 | MR (Reset) | Master Reset (Active High) |
| 15 | CLOCK INHIBIT | Disables Clock When High |
| 16 | VDD | Supply Voltage |
Product Specifications
| Parameter | Value |
|---|---|
| IC Function | 8-bit Parallel-In Serial-Out Shift Register |
| Logic Family | CMOS |
| Package Type | DIP-16 |
| Operating Voltage | 3V – 15V |
| Max Clock Frequency | 8 MHz (typical at 10V) |
| Input Type | CMOS-compatible |
| Output Type | Buffered, TTL-compatible |
| Operating Temperature | -55°C to +125°C |
Applications
Keypad matrix scanning
Digital input expansion for microcontrollers
Remote control systems
Switch status monitoring
Multiplexed sensor input reading
Serial communication of multiple digital signals
Home automation control panels
