74LS139

The 7400 series of chips perform transistor-transistor logic. From Wikipedia, the 74LS series is "Low-power Schottky. Implemented using the same technology as 74S but with reduced power consumption and switching speed, due to larger resistors. Typical 10 ns gate delay, remarkable (for the time) 2 mW dissipation, 4.75–5.25 V." In layman's terms, on SNES PCBs, these chips link together ROM and RAM chips. The 74LS139 chips can be found on PCBs with SRAM.

SN74LS139N

Chip type: 74LS139

Part #: SN74LS139N

Manufacturer: Texas Instruments

Date format: xYWWxxxxx

Variables: Full part #, Date code

MB74LS139

Chip type: 74LS139

Part #: MB74LS139

Manufacturer: Fujitsu

Date format: YYWW xxx

Variables: Date code

SN74LS139AN

Chip type: 74LS139

Part #: SN74LS139AN

Manufacturer: Texas Instruments

Date format: YWWxxxx

Variables: Full part #, Date code

HD74LS139P

Chip type: 74LS139

Part #: HD74LS139P

Manufacturer: Hitachi

Date format: YMW x

Variables: Date code