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Cross-Platform Assembler		Spec File Syntax

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Syntax is based mainly on standard BBC assembly syntax as that is the context this application was originally written for. The following describes the main points:

• Only one command per line is allowed (multiple-command lines make code difficult to read and should be avoided anyway! ;).
• Comments are introduced by a backslash character and extend to the end of the line.
• A label may appear on a line of its own and refers to the next address that would occupy a command.
• Otherwise, a line consists of an optional label followed by a command mnemonic seperated by white space. An optional argument may follow further white space and must match one of the addressing mode patterns in the spec file.
• Mnemonics and psuedo-commands are case insensitive.
• The following pseudo-commands are recognised:

  EQUB

  the arg is a byte to add directly to the output at the current address;

  EQUW

  the arg is a word (2 bytes) to add directly to the output at the current address in machine host byte order;

  EQUR

  the arg is a word to add directly to the output at the current address in high,low byte order;

  EQUS

  the arg is a string (optionally surrounded by double quotes) and the byte codes for each character are added directly to the output at the current address.

• Expressions in arguments (and byte specifiers in the spec file) are allowed as follows:
  • positive and negative integers;
  • "pc" specifies the current program counter (will refer to the address of the first byte of the op-code);
  • (expr) used to group expressions - doesn't work quite how you think so beware!
  • expr + expr specifies the sum of two expressions;
  • expr - expr specifies the difference between two expressions;
  • expr mod expr specifies the first expression modulo the second;
  • expr div expr specifies integer division;
  • &expr means the expression treated as a hex number;
  • asc "x" specifies the ascii code for the character between double quotes;
  • a label will be expanded to its address.
• Fixed address labels can be specified on a line of their own as:

  label=value

  where the value must be preceded by "&" or "0x" to be recognised as hex.

• A label specification within the code must be preceded by a dot and use of a label in an expression must not include the dot.

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Previous page:	Assembler Syntax	Next page:
Cross-Platform Assembler		Spec File Syntax