Differences between the 65C02 and 65C816 Processors in 8-bit Mode #Microprocessors #VintageComputing

Jaroslav Sýkora writes about the 65C02 and the 65C816 CPUs:

In X65 the assembled CPU is either the 8-bit W65C02S or 16-bit W65C816S. The W65C816S is (partially) compatible with W65C02S. This page summarizes the differences from the low-level hardware point of view and in the case that the 65C816 is running in the 8-bit Emulation Mode.

Differences mentioned are quite minor. However, regarding the Instruction Set Architecture (ISA), 32 instructions are different between the processors.

The problematic instructions (from the 65C816 point of view) are the following 65C02 instructions:

RMB0..RMB7 = Reset Memory Bit
SMB0..SMB7 = Set Memory Bit
BBR0..BBR7 = Branch on Bit Set
BBS0..BBS7 = Branch on Bit Reset

If 65C816 (in the Emulation Mode) should run a program originally written for 65C02, these instructions must be replaced with an alternative code.

Read the entire discussion in the post here.


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