6502 Assembler

For simple 6502 online assembly of 6502 code You can use this assembler .. It is limited in that it does not support ASCII (text) storage in memory locations at will ..but can be achieved via .BYTE or .WORD pragmas ...

Here is a snapshot of generated code from a simple assembly program

Follow the instructions on the website re Assembly opcode format ... and some of it is repeated below ...

Syntax

The assembler supports the following syntax:

Opcodes and Addressing

Instructions are always 3 letter mnemonics followed by an (optional) operand/address:

Where HHLL is a 16 bit word and LL or BB a 8 bit byte, and A is literal "A".

There must not be any white space in any part of an instruction's address.

Labels and Identifiers

Identifiers must begin with a letter [A-Z] and contain letters, digits, and the underscore [A-Z0-9_]. Only the first 6 characters are significant.

All identifiers, numbers, opcodes, and pragmas are case insensitive and translated to upper case. Identifiers must not be the same as valid opcodes.

The special identifier "*" refers to the program counter (PC).

White Space

The assembler does not rely on any special formatting with the following exclusion:

There must be white space between a label and a opcode and the opcode and any operands. Only one instruction per line is permitted.

Assembly language programming - online ebook by L.A Leventhal