Adding the s suffix to sub causes it to update the flags itself, based on the result of the operation.
This mechanism is common to many processor architectures, and the semantics if not the details of cmp will likely be familiar. The simplest way to set the condition flags is to use a comparison operation, such as cmp.
The flags indicate simple properties such as whether or not the result was negative, and are used in various combinations to detect higher-level relationships such as "greater than" and suchlike. Previous Part.
All bits must be zero for Z to be 1. Brief Example. Post as a guest Name.
The same applies to using instructions such as LSR, for shifting right. Site Search User.
This bit can be used to implement 64-bit unsigned arithmetic, for example. Specifically, look up section 3-2 and table 3-18 Integer Unit Condition Code Computations , which lists the boolean equations the processor applies to update the CCR state.
The point is, you understand how the 68k can branch off and read other instructions if a byte, word or long-word does not meet the right conditions. Dedicated comparison instructions are therefore quite commonly used. The N flag is set by an instruction if the result is negative.
This post is part of a series: If the result were positive, the Negative flag would be cleared. Up 0 Down Reply More Cancel. Of course, the Architecture Reference Manual is the definitive source of information, so if you need to know about a specific corner-case that I do not cover here, that is where you need to look. In this case, the flags will be set as follows:.