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WDC 65C816

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W65C816S microprocessor in a DIP40 package. The processor is also available in a square LCC.

The WDC 65816 (also: 65C816), a 16-bit microprocessor CPU developed by the Western Design Center (WDC), is an expanded and compatible successor to the venerable MOS Technology 6502. The number 65 in the 65816's name comes from the 6502 compatibility, and 816 signifies that it can work in both 8 and 16 bit modes.

The 65816 was second-sourced by GTE, Sanyo and a couple of other semiconductor companies from the mid-to-late 1980s to the early 1990s. As of 2008, it is still sold by WDC, and the architecture has also been implemented as an IP core in some systems, such as Winbond's W55V9x series of TV Edutainment ICs.

The processor was designed almost entirely by WDC's founder and CEO Bill Mensch, who began work on the chip after consulting Apple Computer in 1982. The only person who aided him in his work was his sister Kathryn who did part of the layout. The chip was finished in March 1984, with samples sent to both Apple and Atari.

CPU features

This list gives the major features of the 65C816S (S = static core):

  • Fully static CMOS design for low power consumption (300 µA @ 1 MHz) and increased noise immunity
  • Wide operating voltage range: 1.8 V ± 5%, 2.5 V ± 5%, 3.0 V ± 5%, 3.3 V ± 10%, 5.0 V ± 5% for use with varying voltage peripherals
  • Emulation mode allows complete software compatibility with the 65C02, excepting undocumented opcodes.
  • 24-bit memory addressing provides access to 16 MB of memory space
  • 16-bit ALU, accumulator, stack pointer and index registers
  • Valid Data Address (VDA) and Valid Program Address (VPA) output for dual cache and cycle steal DMA implementation
  • Vector Pull (VPB) output indicates when interrupt vectors are being addressed
  • Abort (ABORTB) input and associated vector supports processor repairs of bus error conditions
  • Separate program and data bank registers allow program segmentation or full 16 MB linear addressing
  • Direct register and stack relative addressing provides capability for reentrant, recursive and re-locatable programming
  • 24 addressing modes - 13 original 6502 modes with 92 instructions using 256 op codes—including some new opcodes from the 65C02 (not including the zero-page single-bit operations unique to the Rockwell version), and one reserved opcode (WDM—which was later used as an escape instruction in the 32-bit 65C832 design)
  • Wait-for-Interrupt (WAI) and Stop-the-Clock (STP) instructions further reduce power consumption, decrease interrupt latency and allows synchronization with external events
  • Co-Processor (COP) instruction with associated vector supports co-processor configurations, e.g., floating point processors
  • Block move ability

The 65802

The WDC 65802 (also: 65C802) is a 65816 CPU in a 6502-pinout package (fully 6502 compatible). The 65802 was produced by WDC and GTE during the mid-to-late 1980s and early 1990s.

The chip was designed as an upgrade path from the 8-bit 6502/65C02 to the new 65816 16-bit CPU. To do this, the high 8 bits of the 65802's address bus were interleaved onto the data bus lines during phases of the system clock that were considered "unstable territory" on the 6502. Therefore old systems did not use the data bus during those phases. Hardware that expects a 6502 sees a 16-bit address bus, whilst 65802 savvy hardware can pick out and latch the additional address info as it becomes available. (This feature was used by some memory expansion cards.)

Typically, when hardware manufacturers have designed a project from the ground up, they have used the 65816, which offers more straightforward access to the CPU's new features.

Notable uses

A number of SNES games contained the Nintendo SA-1, an upgraded version of the 65816.

References

  • Eyes, David; Lichty, Ron (1986). Programming the 65816 including the 6502, 65C02, and 65802. New York: Brady Books/Prentice Hall Press (Simon & Schuster, Inc). ISBN 0-89303-789-3.

See also


This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

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