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Comparator
3-14
3.3 Comparator
The C614 provides a simple comparator that is enabled by a control register
option. The inputs of the comparator are shared with pins PD
4
and PD
5
. PD
5
is the noninverting input to the comparator, and PD
4
is the inverting input.
When the comparator is enabled, the conditional operation COND2 (normally
associated with PD
1
) becomes associated with the comparator result. In addi-
tion, the interrupts associated with PD
4
and PD
5
(namely, INT6 and INT7), be-
come interrupts based on a
transition
in the comparator result. Finally, the
start/stop function of TIMER1 may be controlled, indirectly, by a comparator
transition. When enabled, therefore, the comparator controls the following four
events:
(1) Steady-State Comparator TRUE V
PD5
> V
PD4
COND2 = TRUE . . .
CIN2
CNIN2
has its conditional call taken.
has its conditional call ignored.
JIN2
JNIN2
has its conditional jump taken.
has its conditional jump ignored.
(2) Steady-State Comparator FALSE V
PD5
< V
PD4
COND2 = FALSE . . .
CIN2
CNIN2
has its conditional call ignored.
has its conditional call taken.
JIN2
JNIN2
has its conditional jump ignored.
has its conditional jump taken.
(3) Comparator transition FALSE-to-TRUE V
PD5
rises above V
PD4
. . .
INT6 trigger event
IF: [(INT6 Flag is SET) OR (INT7 Flag is CLEAR)] AND (TIMER1 Enable is CLEAR)
THEN: TIMER1 stops counting
(4) Comparator transition TRUE-to-FALSE V
PD5
falls below V
PD4
. . .
INT7 trigger event
IF: [(INT6 Flag is CLEAR) AND (INT7 Flag is SET)] OR (TIMER1 Enable is SET)]
THEN: TIMER1 starts counting
With regards to the transition events, the rising-edge in the comparator is a
trigger for INT6. This happens independently of any activity associated with
TIMER1. TIMER1, on the other hand, comes to a stop anytime the following
conditional is true:
IF: [(INT6 Flag is SET) OR (INT7 Flag is CLEAR)] AND (TIMER1 Enable is CLEAR)]
THEN: TIMER1 stops counting
INT6 flag refers to bit 6 within the interrupt flag register (IFR, peripheral port
0x39). This bit is automatically SET anytime that an INT6 event occurs. The