User guide

The available logical operators are:
>> Logical shift right
<< Logical shift left
|| Logical OR
&& Logical AND
^^ Logical Exclusive OR
This will have slightly more use when it comes to inserting the addresses of things, such as:
TXA
STA buffer
TYA
STA [buffer + 1]
The calculation works by extracting the parts of the calculation to a ‘stack’, so our example [12+42-11]
would break down to be:
location: 0 1 2 3 4 5 6 7
value: 12 + 42 - 11 ] x x (‘]’ meaning end and ‘x’ meaning unused)
The stack can hold up to eight items (locations 0 to 7). More complex calculations will be faulted.
Addressing modes (NMOS)
This is a look at the addressing modes provided on the 6502 processor. It is given as a useful reference, and
also to describe how to format instructions that use a particular addressing mode.
Implicit (or Implied) addressing
<instruction>
No value is required. Memory may be referenced, but it will be done in ways you cannot control.
For example PHA will push the contents of the accumulator to the next free stack location.
You can set up the stack, but not with the PHA instruction...
Examples:
CLI
RTS
Accumulator addressing
<instruction> A
The operation is performed with/to the accumulator. The ‘A’ is important, unlike some
assemblers 6502asm will not ‘guess’ whether or not you meant to use the accumulator addressing
mode.
Examples:
ASL A
ROR A
6502asm user guide – prerelease version
page 11