How Intel’s 386 Protects Itself From ESD, Latch-up and Metastability
1 min read
Summary
Intel’s now vintage 386 processor, first launched in 1985, is not only seeing a rebirth in popularity thanks to its use in some modern niche computing devices, but it’s also giving semiconductor engineers the opportunity to study its architecture and create a nod to the past with fresh blog posts and deep-dives.
One such post from computing historian Ken Shirriff highlights the massive I/O pads on the chip, and the vulnerabilities they present.
Each of the 141 golden bond pads are linked to a pin in the packaging via a delicate gold wire, however, electrostatic discharge (ESD) can present a significant risk as it can deliver a high-voltage spike that can literally blow holes in the circuitry; Shirriff explains that the protective circuit used in the 386 employs clamping diodes, current-limiting resistors and a third diode to guard against this.
Latches can also be an issue, but the chip implements ‘guard rings’ to prevent unwanted current flow.
