1. General description
The 74HC194 is a 4-bit bidirectional universal shift register. The synchronous operation of the
device is determined by the mode select inputs (S0, S1). In parallel load mode (S0 and S1 HIGH)
data appearing on the D0 to D3 inputs, when S0 and S1 are HIGH, is transferred to the Q0 to Q3
outputs. When S0 is HIGH and S1 is LOW data is entered serially via DSL and shifted from left
to right; when S0 is LOW and S1 is HIGH data is entered serially via DSR and shifted from right
to left. DSR and DSL allow multistage shift right or shift left data transfers without interfering with
parallel load operation. If both S0 and S1 are LOW, existing data is retained in a hold mode. Mode
select and data inputs are edge-triggered, responding only to the LOW-to-HIGH transition of the
clock (CP). Therefore, the only timing restriction is that the mode control and selected data inputs
must be stable one set-up time prior to the positive transition of the clock pulse. When LOW, the
asynchronous master reset (MR) overrides all other input conditions and forces the Q outputs
LOW. Inputs include clamp diodes. This enables the use of current limiting resistors to interface
inputs to voltages in excess of VCC.
2. Features and benefits
• Wide supply voltage range from 2.0 V to 6.0 V
• CMOS low power dissipation
• High noise immunity
• Latch-up performance exceeds 100 mA per JESD 78 Class II Level B
• Complies with JEDEC standards:
• JESD8C (2.7 V to 3.6 V)
• JESD7A (2.0 V to 6.0 V)
• CMOS input levels
• Shift-left and shift right capability
• Synchronous parallel and serial data transfer
• Easily expanded for both serial and parallel operation
• Asynchronous master reset
• Hold (‘do nothing’) mode
• ESD protection:
• HBM JESD22-A114F exceeds 2000 V
• MM JESD22-A115-A exceeds 200 V
• Specified from -40 °C to +85 °C and -40 °C to +125 °C