User guide
40 Focusing on a Single Device
Time started here.
H1
E1
L1
H2
E2
L2
E1
Timer expires in this range.
Second iteration of timer expires in this range.
Figure 5. Expected, Low, and High Duration of Timeout Events
Accuracy of Second Timers
The second timers rely on the one-second timer, which is based on the millisecond
timer mechanism described earlier. A one-second timer of duration
D
times out
in the range of
D
-1 to
D
seconds, where “second” is defined as 1001 milliseconds
using the millisecond timer duration formulas for
L
and
H
.
For example, at 625 kHz, each “second” is 991.23 milliseconds. Thus a 10-second
timer would time out in the range of 8.74 to 10.09 seconds.
For repeating one-second timers, the first timeout occurs in the range of
D
-1 to
D
seconds. Subsequent timeouts occur every
D
seconds. The fifth timeout of a
repeating 10-second timer would occur in the range of 48.39 to 49.74 seconds.
Delay Functions
Three functions allow an application to perform timing directly by suspending
execution for a given time. These functions provide a concise way to perform
timing in-line:
delay( )
msec_delay( )
scaled_delay( )
The delay( ) function produces a delay of fixed duration that is independent of
input clock speed. This function can be used with the wink feature and for I/O
debouncing. Its prototype is the following:
void delay (unsigned long
count
);