Page 121 - Understanding Automotive Electronics

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4 MICROCOMPUTER INSTRUMENTATION AND CONTROL

Figure 4.5
Use of the CC
Register

FPO

Program branches are either conditional or unconditional. Eight of the
nine branch instructions listed in Figure 4.5b are conditional branches. That is
to say, the branch is taken only if certain conditions are met. These conditions
are indicated by the CC register bit as shown. The branch-always instruction is
the only unconditional branch. Such a branch is used to branch around the
next instruction to a later instruction or to return to an earlier instruction.
Another type of branch instruction that takes the computer out of its normal
program sequence is indicated for the I bit of the CC register. It is associated
with an interrupt. An interrupt is a request, usually from an input or output (I/
O) peripheral, that the CPU stop what it is doing and accept or take care of
(service) the special request. There will be more about interrupts later in this
chapter.

108 UNDERSTANDING AUTOMOTIVE ELECTRONICS