This directive turns assembler options on and off.
OPT option[,option,...]
The OPT directive is used to designate the Assembler options. Assembler options are given in the operand field of the source input file and are separated by commas. All options have a default condition. Some options are reset to their default condition at the end of pass one. Some are allowed to have the prefix NO attached to them, which then reverses their meaning.
OPT cc, NOW