NXP HEF4094BP 8-Stage Shift-and-Store Register IC: Datasheet, Pinout, and Application Circuit Guide
The NXP HEF4094BP is a versatile 8-stage serial-in, serial-or-parallel-out shift register with a storage register and three-state outputs. This CMOS IC is widely used for data expansion, serial-to-parallel conversion, and controlling multiple outputs with a minimal number of microcontroller GPIO pins. Its ability to drive high-current loads makes it suitable for interfacing with LEDs, relays, and other peripherals.
Datasheet Overview
Key specifications from the datasheet include a wide supply voltage range from 3V to 15V, low power consumption thanks to its CMOS technology, and high noise immunity. It features a maximum clock frequency of typically 12 MHz (at 10V). The three-state outputs allow the bus-oriented design to be connected to other similar devices or microcontrollers efficiently. The device operates over a broad temperature range, making it robust for industrial applications.
Pinout Configuration
The HEF4094BP is housed in a 16-pin DIP package. Its pinout is crucial for proper circuit design:
Pin 1 (Output Enable - OE): Controls the three-state outputs. A high level enables the outputs; a low level sets them to a high-impedance state.
Pin 2 (Data Serial Output - QS1): Provides the data from the eighth shift register stage for cascading multiple devices.
Pin 3 (Data Serial Output - QS2): Offers the data from the eighth shift register stage one clock cycle earlier than QS1, useful for synchronization.
Pin 4 (Serial Data Input - DATA): The primary serial data input fed into the first stage of the shift register.
Pin 5 (Clock Input - CP): The shift register clock signal. Data is shifted on the low-to-high (positive) clock transition.
Pin 6 (Strobe Input - STR): Also known as the Latch Enable. A high-to-low transition transfers the data from the shift register stages to the storage register (output latches).
Pins 7, 8, 9, 10, 11, 12, 13, 14 (Parallel Outputs Q1 to Q8): The buffered outputs from the storage register.
Pin 15 (Reset - MR): A low pulse on this pin asynchronously clears all stages of the shift register (but not the storage register).
Pin 16 (VDD): Positive supply voltage.
Pin 8 (VSS): Ground.
Application Circuit Guide
A typical application involves using the HEF4094BP as an I/O expander for a microcontroller. Here’s a basic connection guide:
1. Connect the DATA, CP, and STR pins to three separate GPIO pins of a microcontroller (e.g., an Arduino or MCU).
2. Connect the OE pin to a GPIO pin or directly to VDD if constant output enable is desired.
3. Connect the MR pin to VDD or a GPIO pin if reset functionality is needed.
4. Link VDD to the system’s positive rail (e.g., 5V) and VSS to ground.
5. Connect the desired loads (e.g., LEDs with current-limiting resistors) to the parallel outputs (Q1-Q8).
Operation Sequence:
To output a specific pattern (e.g., 0b10101100):
Set STR low to disable the output latches from updating.
The microcontroller shifts out each bit of the data byte one by one to the DATA pin, toggling the CP pin high then low for each bit.
After all 8 bits are shifted in, pulse the STR pin high then low. This latches the data from the internal shift register into the storage register, instantly updating all parallel outputs (Q1-Q8) to the new pattern.
The OE pin can be used to turn all outputs on or off without changing the stored data.
Multiple HEF4094BP chips can be easily cascaded by connecting the QS1 or QS2 output of the first IC to the DATA input of the next one, allowing control of virtually any number of outputs with the same three microcontroller pins.
The NXP HEF4094BP remains a highly effective and reliable solution for expanding digital output capabilities. Its integrated output latches and three-state control provide flexibility for complex applications, from simple LED displays to sophisticated industrial control systems. Its ease of use and daisy-chaining capability make it a fundamental component in a digital designer's toolkit.
Keywords: Shift Register, Serial-to-Parallel Converter, Output Expander, CMOS IC, Three-State Outputs
