# SN54ALS191A, SN74ALS191A

## Description
Synchronous 4-bit reversible up/down binary counters. Eliminates counting spikes associated with asynchronous counters.

## Features
️· Synchronous operation
️· Fully synchronous in count modes
️· Asynchronously resettable with load control
️· Programmable – preset capability
️· Cascading capability with ripple clock and max/min outputs
️· Independent clock circuit

## Electrical Characteristics
️· Supply Voltage (VCC): 4.5V to 5.5V
️· Input High Voltage (VIH): 2V
️· Input Low Voltage (VIL): 0.7V/0.8V

## Logic Diagram
Four flip-flops clocked simultaneously. Inputs include: Clock (CLK), Count Enable (CTEN), Down/Up (D/U), Load, Data inputs (QA, QB, QC, QD), Ripple Clock Output (RCO), Max/Min Output.

## Absolute Maximum Ratings
️· VCC: 7V
️· VI: 7V
️· Operating Temperature: -55°C to 125°C (SN54ALS191A), 0°C to 70°C (SN74ALS191A)

## Switching Characteristics
️· Propagation Delay (tPLH, tPHL): Varies depending on input/output combination (typically 3-37ns)
️· Clock Frequency: Up to 30 MHz

## Package Options
️· Plastic Small Outline (D)
️· Ceramic Chip Carriers (FK)
️· Plastic DIP (N)
️· Ceramic DIP (J)