1. General description
The 74HC299 is an 8-bit universal shift register with 3-state outputs. It contains eight
edge-triggered D-type flip-flops and the interstage logic necessary to perform synchronous
shift-right, shift-left, parallel load and hold operations. The type of operation is determined by the
mode select inputs S0 and S1. Pins I/O0 to I/O7 are flip-flop 3-state buffer outputs which allow
them to operate as data inputs in parallel load mode. The serial outputs Q0 and Q7 are used for
expansion in serial shifting of longer words. A LOW signal on the asynchronous master reset
input MR overrides the Sn and clock CP inputs and resets the flip-flops. All other state changes
are initiated by the rising edge of the clock pulse. Inputs can change when the clock is either
state, provided that the recommended set-up and hold times are observed. A HIGH signal on
the 3-state output enable inputs OE1 or OE2 disables the 3-state buffers and the I/On outputs
assume a high-impedance OFF-state. In this condition, the shift, hold, load and reset operations
can still occur. The 3-state buffers are also disabled by HIGH signals on both S0 and S1, when
in preparation for a parallel load operation. 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
• CMOS input levels
• Multiplexed inputs/outputs provide improved bit density
• Four operating modes:
• Shift left
• Shift right
• Hold (store)
• Load data
• Operates with output enable or at high-impedance OFF-state
• 3-state outputs drive bus lines directly
• Cascadable for n-bit word lengths
• ESD protection:
• HBM JESD22-A114F exceeds 2000 V
• MM JESD22-A115-A exceeds 200 V
• Specified from -40 °C to +85 °C and from -40 °C to +125 °C