8-Bit Shift/Store Register with Three-State Outputs# Technical Documentation: MC14094BFEL 8-Stage Shift-and-Store Bus Register
Manufacturer : ON Semiconductor
Component Type : CMOS 8-Stage Shift-and-Store Bus Register with Three-State Outputs
Package : SOIC-16
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## 1. Application Scenarios
### Typical Use Cases
The MC14094BFEL is a versatile CMOS integrated circuit primarily employed in digital systems requiring serial-to-parallel data conversion with temporary storage capability. Its integrated three-state outputs make it particularly valuable for bus-oriented architectures.
Primary Functions:
* Serial-to-Parallel Data Conversion: A serial data stream applied to the Data input is shifted through the internal 8-stage shift register on each rising edge of the Clock (CP) signal. The parallel data is then available at the outputs (Q1-Q8) after a load operation.
* Data Storage/Latching: The device features a separate "Store" (or "Strobe") clock input. When pulsed, it transfers the data currently present in the shift register stages into an independent 8-bit latch. This allows new data to be shifted in via the serial input without disturbing the currently outputted parallel data.
* Bus Interface: The three-state outputs enable direct connection to a shared data bus. When the Output Enable (OE) pin is driven low, the latched data is presented to the bus. When OE is high, the outputs enter a high-impedance state, effectively disconnecting the device from the bus.
### Industry Applications
1. Microcontroller/Microprocessor Peripheral Expansion: Commonly used to add multiple parallel output ports using only a few GPIO pins of a microcontroller (e.g., for driving LEDs, relays, or display segments). The microcontroller sends data serially to one or more cascaded MC14094s.
2. Industrial Control Systems: Drives banks of indicators, solenoid valves, or solid-state relays in PLCs and control panels, where centralized serial control simplifies wiring.
3. Instrumentation and Display Drivers: Controls multi-digit 7-segment LED displays or annunciator panels. Multiple devices can be daisy-chained to control extensive display arrays.
4. Data Acquisition Systems: Functions as a serial-in, parallel-out buffer for setting digital control words for DACs, digital potentiometers, or other programmable devices on a shared bus.
5. Communication Interfaces: Can be used in simple serial peripheral interfaces to expand I/O, often in cost-sensitive designs where a full SPI or I²C peripheral is not available or necessary.
### Practical Advantages and Limitations
Advantages:
* Pin Efficiency: Drastically reduces the number of microcontroller I/O pins required to control multiple outputs.
* Non-Destructive Readout: The separate store register allows the shift register to be reloaded with new data while the current output data remains stable, preventing glitches on output lines.
* Bus Compatibility: Three-state outputs facilitate safe connection to bidirectional data buses, supporting multiple drivers.
* Cascadability: Multiple devices can be easily connected in series to create 16-, 24-, or larger bit registers.
* Wide Voltage Range: Standard CMOS operation from 3.0V to 18V DC, making it compatible with TTL (at 5V) and higher voltage industrial logic.
Limitations:
* Speed: Compared to modern high-speed shift registers (e.g., 74HC series), the 4000-series CMOS is relatively slow (typical clock frequency ~8-12 MHz at 10V). It is not suitable for high-speed serial data links.
* Output Current: Sink/source current capability is limited (e.g., ~8 mA at 5V). Driving heavy loads like multiple LEDs or relays requires external buffer transistors or drivers.
* Power Consumption:
