NEC V20

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The NEC V20 (μPD70108) was a processor made by NEC that featured approximately 29,000 transistors. It was a reversed-engineered, pin-compatible version of an Intel 8088 processor (code compatible with the Intel 80186) that ran at 8 to 12 megahertz. The design was more efficient than the 8088 and caused the V20 to run 30% faster. The main feature that made it run faster was that it had hardware for multiplication, whereas the Intel chips had to do multiplication in microcode software. It was used in "turbo" versions of some PC clones such as Copam and Tandy 1110 laptop series. Sony also produced this microprocessor under license from NEC as the V20H.

An unusual feature of the NEC V20 was that it added an Intel 8080 emulation mode, in which it could execute programs written for the Intel 8080 processors. The instructions BRKEM executed in 8086 mode (NEC used a different notation for the instructions than Intel and BRK in NEC notation = INT in Intel notation) and RETEM and CALLN executed in 8080 mode was used to switch/return to/from the emulation mode.

The NEC V30 (μPD70116) was a version of the NEC V20 that was pin compatible with the 16-bit data bus Intel 8086 processor.

The NEC V25 is the microcontroller version of the NEC V20 processor.

The NEC V33 is a super version of the V30 that separates address bus and data bus, and executes all instructions with wired logic instead of micro-codes, making it twice as fast as a V30 for the same clock frequency. V33 has the performance equivalent to Intel 80286. NEC V33 has two additional instructions BRKXA and RETXA to support extended addressing mode. The emulation mode was not supported.

The NEC V33A (μPD70136A) differs from the NEC V33 in that is has interrupt vector number compatible with intel 80X86 processors

NEC V40 (μPD70208) embedded version of V20, integrated i8251, i8253 and i8255

NEC V50 (μPD70216) embedded version of V30 with 16-bit data bus

The NEC V41 (μPD70270) NEC V51 (μPD70280) integrated V30HL core and PC-XT peripherals: 8255 PIO, 82c54 timer, 8259 PIC, 8237 DMA controller and PS/2 keboard interface. Also integrates full DRAM controller. Was used in Olivetti Quaderno XT-20.

The NEC V53 integrates some peripherals with a V33 core.

The NEC V53A (μPD70236A) integrates some peripherals with a V33A core.