Here be dragons: Preventing static damage, latchup, and metastability in the 386
12 hours ago
- The Intel 386's I/O pins face three major dangers: static electricity, latchup, and metastability, requiring specialized protection circuits.
- Protection against static electricity uses diodes and resistors to divert excess voltage and limit current, preventing damage to the thin oxide layer.
- Latchup is caused by parasitic transistors forming a feedback loop; guard rings around I/O transistors block unwanted currents and prevent short circuits.
- Metastability occurs when an input signal changes near a clock edge, causing an indeterminate state; a synchronizer with two flip-flops reduces the risk, using a sense-amplifier flip-flop for faster resolution.
- The I/O circuits are fundamentally different from internal logic, blending analog and digital design to defend against these 'dragons'.