1. 656L38D4C3T Substitution Conclusion Full substitution is permissible. The 656L38D4C3T is fully compatible with the original part number in all core electrical specifications (frequency, voltage, output type, functionality), physical footprint, and current consumption. Its primary and sole enhancement is an improvement in frequency stability from ±50ppm to a superior ±30ppm. This model offers higher timing accuracy and better temperature stability. It represents a direct performance upgrade while meeting all original design requirements. Post-replacement, the system clock signal quality will be improved without requiring any design modifications.