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When migrating assembly language programs from one family of microcontrollers to another, the first question is almost always: “What’s the equivalent opcode?” Some operations, like addition and subtraction, are self-evident and practically universal. Other instructions may have some subtle differences in syntax or spelling that make direct conversions a bit trickier. Occasionally, some instructions simply don’t have a direct equivalent in the target set, or an equivalent exists but is explained in different terms. Another question that arises is that of addressing modes. Typically, Direct and Indirect Addressing modes are standard in all architectures. However, they tend to be different in limitations and feature set. To help simplify the conversion process, this application note provides a table of the instruction set of the 8051 8-bit microcontroller family and their equivalents in the PICmicro® instruction sets (Table 1). It is organized alphabetically by the 8051 instruction mnemonic in the first column, followed by the common description of the operation and the closest equivalent opcode or opcode sequence in the Microchip PIC16 and PIC18 instruction sets. In addition, the size of the instructions (in words or bytes, as appropriate) and the number of machine or instruction cycles required for execution are listed for each entry.

Converting from 8051 to Microchip Assembler: A Quick Reference (.pdf) - Microprocessors and Microcontrollers