| Technology Family | LS |
| Function | Digital Multiplexer |
| Configuration | 2:1 |
| Number of channels (#) | 4 |
| Operating temperature range (C) | -55 to 125 |
| Rating | Military |
- Single-Rail Outputs on 'LS399
- Selects One of Two 4-Bit Data Sources and Stores Data Synchronously with System Clock
- Applications:
- Dual Source for Operands and Constants in Arithmetic Processor; Can Release Processor Register Files for Acquiring New Data
- Implement Separate Registers Capable of Parallel Exchange of Contents Yet Retain External Load Capability
- Universal Type Register for Implementing Various Shift Patterns: Even Has Compound Left-Right Capabilities
This monolithic quadruple two-input multiplexer with storage provides essentially the equivalent functional capabilities of two separate MSI functions (SN54LS157/SN74LS157 and SN54LS175/SN74LS175) in a single 16-pin package.
When the word-select input is low, word 1 (A1, B1, C1, D1) is applied to the flip-flops. A high input to word select will cause the selection of word 2 (A2, B2, C2, D2). The selected word is clocked to the output terminals on the positive-going edge of the clock pulse.
Typical power dissipation is 37 milliwatts. The SN54LS399 is characterized for operation over the full military range of -55°C to 125°C. The SN74LS399 is characterized for operation from 0°C to 70°C.