Assembler Syntax
================

Instructions
~~~~~~~~~~~~ 
add     [A|B|X],[constant|address]              ;[I|M|(M)|M+X|(M)+X]
sub     [A|B|X],[constant|address]              ;
load    [A|B|X],[constant|address]              ;
store   [A|B|X],[constant|address]              ;
and     [A],[constant|address]                  ;
or      [A],[constant|address]                  ;
lneg    [A],[constant|address]                  ;

jmp     [A|B|X],[NE|EQ|LT|GE|GT|GLE],address    ;[M|(M)]
jmk     [A|B|X],[NE|EQ|LT|GE|GT|GLE],address    ;

skp     [7|6|5|5|4|3|2|1|0],[0|1],address       ;[M]
set     [7|6|5|5|4|3|2|1|0],[0|1],address       ;

sft     [A|B],[L|R],[1|2|3|4]
rot     [A|B],[L|R],[1|2|3|4]

nop
halt

org     constant                                ;[I]

Directives
~~~~~~~~~~
        org     constant                        ;[I] 
label   [blank|instruction|constant]            ;[I] 
        constant                                ;[I]
        db      constant                        ;[I]
         
The org directive can appear anywhere to set the starting instruction address
for all instructions that follow. If a constant is not present address 4 is 
assumed.

The db directive will reserve a byte of memory at the address at which it is 
defined. You add a constant operand to reserve multiple bytes.

If the OpCode position has an Integer Constant, then the value of that constant
is placed at the current address, and the program counter is advanced by one. 

Notes
~~~~~

* Any text appearing after a semi-colon (;) on a line will be considered a 
  comment and be ignored.

* All OpCodes, operands, and labels are NOT case sensitive.
 
* A line of assembly code consists of:
    - whitespace (spaces and tabs) OR an optional label followed by whitespace,
    - an OpCode followed by whitespace,
    - optional comma separated operands.
  
* Labels must start in column 1 and must begin with a letter. A label can stand
  alone on a line or can be followed by an OpCode or an Integer Constant. 
  Labels are used to determine a specific instruction address. An offset can be 
  added to a label's value when it is used and is defined by appending a + sign 
  followed by an Integer Constant, for example label+3.

* For addresses:
   I    - Immediate (Integer Constant)
   M    - Memory
  (M)   - Indirect
  M+X   - Indexed
 (M)+X  - Indirect Indexed
 
  All of the special memory locations have a reserved address name:
  
      Name      Address         Usage
      ~~~~      ~~~~~~~         ~~~~~
      A         000             A register.
      B         001             B register.
      X         002             C register.
      PC        003             Program counter.
      OUTPUT    128             Maps to front panel data display lamps.
      OCA       129             Overflow/Carry bits for A register.
      OCB       130             Overflow/Carry bits for B register.
      OCX       131             Overflow/Carry bits for X register.
      INPUT     255             Maps to the front panel data input buttons.

  Any address M beginning with a letter is assumed to be a label associated 
  with the actual memory address who's value, obtained using the appropriate 
  addressing mode, will be used in the operation. Any address beginning with 
  a digit or a dash is assumed to be an Integer Constant representing the 
  actual value to be used.
 
* For jumps:
   NE   - Not equal to zero
   EQ   - Equal to zero
   LT   - Less than zero
   GE   - Greater than or equal to zero
   GT   - Greater than zero
   GLE  - Unconditional (greater or less or equal to zero)
   
   For an uncoditional jump you can just use the address alone. It's the same
   as using A,GLE,address.

* Integer Constants:
  Decimal - Decimal integers begin with a non-zero digit followed by zero or
            more decimal digits (0–9).
  Octal   - Octal integers begin with zero (0) followed by zero or more octal
            digits (0–7).
  Binary  - Binary integers begin with “0b” or “0B” followed by one or more
            binary digits (0, 1).
  Hex     - Hexadecimal integers begin with “0x” or “0X” followed by one or
            more hexadecimal digits (0–9, A–F). Hexadecimal digits can be 
            either uppercase or lowercase.
  Char    - Character values begin with a ' followed by a single character.
  Label   - Label address values begin with a # followed by a valid label.
            
  Decimal Integer Constants can have a leading dash (-) to indicate a negative
  number.