What are the differences between high-speed I/O and ordinary I/O EMC in a smart controller PAC?

The EMC design of high-speed I/O (such as pulse output and encoder input) and ordinary I/O (such as digital input and output) of intelligent controllers (PACs) differs significantly. High-speed I/O operates at high frequencies (>1MHz), requiring a focus on signal integrity and radiated emissions. Differential transmission, impedance matching (e.g., 100Ω differential), and equal-length wiring are employed in the design, along with the use of common-mode inductors (CMZ2012A-900T) to suppress common-mode radiation. Ordinary I/O operates at lower frequencies, primarily requiring consideration of immunity, and employs RC filtering, TVS protection (SMBJ6.5CA), and optocoupler isolation.

Regarding power supply, high-speed I/O requires an independent power plane and enhanced decoupling (0.1μF capacitors near the pins); ordinary I/O can share a power supply but requires a series ferrite bead (PBZ1608A-102Z0T). In terms of layout, high-speed I/O should be kept away from sensitive circuits, while ordinary I/O can be centrally located. Tests show that the radiated emissions of high-speed I/O must meet EN55032 Class B, and the immunity of ordinary I/O must pass the IEC61000-4-4 EFT 4kV test.