WDC 65C816
The W65C816S (also 65C816 or 65816) is a 16-bit microprocessor (MPU) developed and sold by the Western Design Center (WDC). Introduced in 1983, the W65C816S is an enhanced version of the WDC 65C02 8-bit MPU, itself a CMOS enhancement of the venerable MOS Technology 6502 NMOS MPU. The 65C816 is the CPU for the Apple IIGS and, in modified form, the Super Nintendo Entertainment System.
PDIP40 package | |
| General information | |
|---|---|
| Launched | 1985 |
| Common manufacturer(s) |
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| Performance | |
| Max. CPU clock rate | 1 MHz to 14 MHz |
| Data width |
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| Address width | 24 |
| Architecture and classification | |
| Instruction set | 6502 |
| Number of instructions | 92 |
| Physical specifications | |
| Package(s) | |
| History | |
| Predecessor(s) |
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| Successor(s) | WDC 65C832 (never released) |
The 65 in the part's designation comes from its 65C02 compatibility mode, and the 816 signifies that the MPU has selectable 8- and 16-bit register sizes. In addition to the availability of 16-bit registers, the W65C816S extends memory addressing to 24 bits, supporting up to 16 megabytes of random-access memory. It has an enhanced instruction set and a 16-bit stack pointer, as well as several new electrical signals for improved system hardware management.
At reset, the W65C816S starts in "emulation mode", meaning it substantially behaves as a 65C02. Thereafter, the W65C816S may be switched to "native mode" with a two instruction sequence, causing it to enable all enhanced features, yet still maintain a substantial degree of backward compatibility with most 65C02 software. However, unlike the PDIP40 version of the 65C02, which is a pin-compatible replacement for its NMOS ancestor, the PDIP40 W65C816S is not pin-compatible with any other 6502 family MPU.
The W65C802 or 65802 is completely software-compatible with the 65C816, but is electrically-compatible with the 6502 and 65C02. Hence the 65C802 could be used as a drop-in replacement in most systems equipped with a 6502 or 65C02. However, the 65C802 cannot emit a 24-bit address, which limits it to a 64 KB address space. The 65C802 is no longer produced.