1 x 8:1 multiplexer in 16-pin DIP
The SN74ALS251N is a single 8:1 multiplexer from Texas Instruments' 74ALS family, packaged in a 16-pin plastic DIP (0.300" width) for through-hole assembly. It selects one of eight data inputs based on a three-bit address and presents it at the output, with a tristate output enable for bus-oriented applications. The commercial temperature range (0°C to 70°C) suits indoor equipment and benchtop instrumentation.
Output drive and signal integrity
The 24 mA low-level output current (IOL) is the figure that governs the fan-out and bus drive capability. At VOL = 0.5 V max, the output can sink 24 mA into a terminated line or multiple LSTTL loads without exceeding the DC noise margin. The 2.6 mA high-level output (IOH) at VOH = 2.7 V min is typical for ALS logic — adequate for driving CMOS inputs with a pull-up but not intended for 50 Ω backplane termination. The tristate output enable (active-low) allows the multiplexer to share a data bus with other outputs. When disabled, the output enters a high-impedance state, preventing bus contention. The propagation delay from address to output is typically 12 ns at 5 V, 25°C — fast enough for 8 MHz address-multiplexed buses in legacy 8-bit processor systems.
The device is ROHS3 compliant, meeting the EU RoHS exemption-free requirements for lead-free assembly. No REACH or UL certification is documented in the available records.