Description:

XT/286, Fujitsu MB671301U Gate Array Based Chipset

This ia an AT 286 chipset that uses a Fujitsu MB671301U gate array for some functions.

Missing from motherboards are the following chips that are usually found in an AT chipset:

• Texas Instruments SN74LS612N (Memory Mapper)
• Intel 82284 (Clock Generator and Ready Interface)
• Intel 82288 (Bus Controller)
• Intel 8254-2 (Programmable Interval Timer)
• Intel 8042 (Keyboard Controller)
• Motorola MC146818P (Real-Time Clock + RAM)

The Intel 8255A-5 (Programmable Peripheral Interface) handles the keyboard interface replacing the 8042, indicating the interface is XT compatible. It is also missing one of the two 8259A chips usually found in an AT, the same for the 8237A. Along with the 8-bit only ISA slots makes this a combination XT-AT chipset. Based on an XT but with a 286 chip. The Real-Time Clock is likely absent as it would be on a XT. The functions provided by the rest of the chips listed above must therefore be performed by the Fujitsu MB671301U gate array.

This chipset, and therefore the MB671301U chip are likely the same as this chipset. At present it is unknown if the chips are pin compatible.

Documented parts

• (any brand) Discrete Logic
• Fujitsu MB671301U
• Intel 8237A-5 (DMA Controller) (known as: VLSI VL82C37A [5-8MHz CMOS Direct Memory Access (DMA) Controller])
• Intel 8253-5 (Programmable Interval Timer)
• Intel 8255A-5 (Programmable Peripheral Interface)
• Intel 8259A-2 (Programmable Interrupt Ctrl.) (known as: VLSI VL82C59A [8-10MHz CMOS Programmable Interrupt Controller], OKI M82C59A-2 [8-10MHz CMOS Programmable Interrupt Controller])