8-bit static shift register for GPIO expansion and daisy-chain data capture
The Texas Instruments CD4021BE is an 8-bit static shift register from the 4000B CMOS logic family. It accepts data in parallel (from eight input pins) or serial-in, and shifts it out serially on a push-pull output — a standard building block for expanding microcontroller GPIO or capturing multiple switch/encoder states over a single wire. The 3V to 18V supply range means it works in 5V, 12V, or unregulated battery systems without a level shifter, and the -55°C to 125°C military temperature grade suits avionics, satellite, and downhole instrumentation where the board sees extreme thermal cycling.
Supply range and temperature — the two specs that decide fit
The 3V to 18V supply range covers 5V, 12V, and unregulated battery systems.
That means Texas Instruments still manufactures it, there is no last-time-buy window closing, and it is not being end-of-lifed. The 4000B series has been in production for decades, and the through-hole DIP variants tend to stay active longer than their surface-mount counterparts because industrial and military customers keep ordering them.