74194 - 4-Bit Bidirectional Universal Shift Register

Overview

The 74194 is a high-speed 4-bit bidirectional universal shift register designed to meet the needs of system designers requiring versatile data handling capabilities. This integrated circuit combines parallel and serial data transfer modes with bidirectional shifting functionality, making it suitable for a wide range of applications in digital systems. The device features synchronous operation with four distinct modes controlled by select inputs, including parallel load, right shift, left shift, and hold (do nothing) states.

Key Features

• Bidirectional Operation: Supports both right-shift and left-shift data movement
• Parallel Loading: Direct input of all 4 bits simultaneously
• Multiple Operating Modes: Four distinct functions controlled by mode select inputs
• Asynchronous Master Reset: Clears all flip-flops regardless of clock state
• High-Speed Operation: Typical clock frequency of 36MHz
• Wide Operating Voltage: Compatible with standard TTL logic levels (4.75V to 5.25V)
• Serial Inputs: Separate pins for right-shift and left-shift data entry
• Parallel Outputs: Buffered outputs for driving standard TTL loads

Applications

The 74194's versatile functionality makes it suitable for numerous digital system applications:

• Data Storage and Transfer: Temporary storage in arithmetic/logic units
• Serial-to-Parallel Conversion: Interface between serial and parallel systems
• Parallel-to-Serial Conversion: Data transmission systems
• Sequence Generators: Pattern generation for control systems
• Delay Element: Digital signal delay circuits
• Ring Counters: Circular shift register applications
• Bus Systems: Data routing in microprocessor systems

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (Vcc): 7V
• Input Voltage: 5.5V
• Operating Temperature Range: 0°C to +70°C
• Storage Temperature Range: -65°C to +150°C

Recommended Operating Conditions

• Supply Voltage (Vcc): 4.75V to 5.25V
• High-Level Input Voltage: 2V min
• Low-Level Input Voltage: 0.8V max
• Clock Frequency: 0 to 36MHz
• Input Rise/Fall Time: 20ns max

DC Characteristics

• High-Level Output Voltage: 2.4V min (Ioh = -0.4mA)
• Low-Level Output Voltage: 0.4V max (Iol = 16mA)
• Input Clamp Voltage: -1.5V max (Iik = -18mA)
• Power Supply Current: 34mA max (all outputs high)

AC Characteristics

• Propagation Delay (Clock to Output): 22ns max
• Propagation Delay (Clear to Output): 27ns max
• Setup Time (Data to Clock): 20ns min
• Hold Time (Data after Clock): 5ns min
• Clock Pulse Width: 25ns min

Functional Description

The 74194 operates as a 4-bit universal shift register with four distinct modes of operation determined by the state of two mode control inputs (S0 and S1). The functional modes are:

• Hold (No Change): S0=0, S1=0 - Outputs remain in current state
• Shift Right: S0=1, S1=0 - Data moves from Q0 toward Q3 (DSR input)
• Shift Left: S0=0, S1=1 - Data moves from Q3 toward Q0 (DSL input)
• Parallel Load: S0=1, S1=1 - Data inputs A-D loaded to outputs Qa-Qd

The master reset (MR) input, when low, clears all flip-flops asynchronously, overriding all other inputs. All operations are synchronized by the rising edge of the clock (CP) input.

Pin Configuration

16-Pin DIP Package

• Pin 1: Clear (MR) - Active low master reset
• Pin 2: Right Shift Data Input (DSR)
• Pin 3: Parallel Data Input A
• Pin 4: Parallel Data Input B
• Pin 5: Parallel Data Input C
• Pin 6: Parallel Data Input D
• Pin 7: Left Shift Data Input (DSL)
• Pin 8: Ground
• Pin 9: Mode Select S0
• Pin 10: Mode Select S1
• Pin 11: Clock (CP) - Positive edge triggered
• Pin 12: Output QD
• Pin 13: Output QC
• Pin 14: Output QB
• Pin 15: Output QA
• Pin 16: Vcc (+5V)

Package Information

The 74194 is available in several standard package options:

• 16-pin Plastic DIP (PDIP): 0.3" wide, industry-standard through-hole package
• 16-pin SOIC: Surface-mount package, 0.154" body width
• 16-pin TSSOP: Thin shrink small-outline package, 0.173" body width

All packages feature lead-free options and are RoHS compliant. The device is rated for commercial temperature range (0°C to +70°C).

Design Considerations

When implementing the 74194 in circuit designs, consider the following:

• Ensure proper decoupling capacitors (0.1μF) are placed near the Vcc pin
• Unused inputs should be tied to either Vcc or ground as appropriate
• For cascading multiple devices, connect QD of one stage to DSR of the next for right-shift operation
• For left-shift cascading, connect QA to DSL of the previous stage
• Observe maximum fan-out limitations when driving multiple TTL loads

Conclusion

The 74194 bidirectional universal shift register provides system designers with a flexible, high-performance solution for data handling applications. Its combination of parallel and serial operations with bidirectional capability makes it particularly valuable in complex digital systems. With proper implementation and attention to timing requirements, the 74194 can serve as a fundamental building block in numerous digital circuit applications.