Unusual circuits in the Intel 386's standard cell logic
a day ago
- #Standard Cell Logic
- #CMOS Technology
- #Intel 386
- The Intel 386 processor, introduced in 1985, was Intel's most complex processor at the time with 285,000 transistors.
- To manage complexity and meet schedules, the 386 team adopted standard cell logic, automating the layout process with computer software.
- Standard cell logic involves using predefined circuits (standard cells) for logic elements, enabling faster chip layout through automatic placement and routing.
- The 386's standard cell circuitry includes unexpected elements like large multiplexers, a transistor outside standard cell layout, and inverters that function differently.
- Multiplexers in the 386 use CMOS switches for efficient signal selection, avoiding large AND/OR gates and improving performance.
- A unique PMOS transistor was found outside standard cell columns, possibly a manual fix to avoid regenerating the entire layout.
- Some inverters in the 386 were actually pairs of independent NMOS and PMOS transistors, used to extend multiplexer functionality.
- Standard cell logic and automatic place and route were pivotal in the 386's success, completed ahead of schedule and defining 32-bit computing dominance.