def _isValidOpcodeByte(sOpcode):
    """
    Checks if sOpcode is a valid lower case opcode byte.
    Returns true/false.
    """
    if len(sOpcode) == 4:
        if sOpcode[:2] == '0x':
            if sOpcode[2] in '0123456789abcdef':
                if sOpcode[3] in '0123456789abcdef':
                    return True;
    return False;