COP881C Datasheet, PDF (16/30 Pages) National Semiconductor (TI) – Microcontrollers

Functional Description (Continued)
TABLE V Timer Operating Modes
CNTRL
Bits
765
Operation Mode
T Interrupt
000
001
010
011
100
101
110
111
External Counter W Auto-Load Reg
External Counter W Auto-Load Reg
Not Allowed
Not Allowed
Timer W Auto-Load Reg
Timer W Auto-Load Reg Toggle TIO Out
Timer W Capture Register
Timer W Capture Register
Timer Underflow
Timer Underflow
Not Allowed
Not Allowed
Timer Underflow
Timer Underflow
TIO Pos Edge
TIO Neg Edge
Timer
Counts
On
TIO Pos Edge
TIO Neg Edge
Not Allowed
Not Allowed
t_C
t_C
t_C
t_C
TL DD 10802–11
FIGURE 9 Timer Counter Auto
Reload Mode Block Diagram
TIMER PWM APPLICATION
Figure 11 shows how a minimal component D A converter
can be built out of the Timer-Register pair in the Auto-Re-
load mode The timer is placed in the ‘‘Timer with auto re-
load’’ mode and the TIO pin is selected as the timer output
At the outset the TIO pin is set high the timer T1 holds the
on time and the register R1 holds the signal off time Setting
TRUN bit starts the timer which counts down at the instruc-
tion cycle rate The underflow toggles the TIO output and
copies the off time into the timer which continues to run By
alternately loading in the on time and the off time at each
successive interrupt a PWM frequency can be easily gener-
ated
TL DD 10802–12
FIGURE 10 Timer Capture Mode Block Diagram
TL DD 10802 – 13
FIGURE 11 Timer Application
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