Parallax BASIC Stamp 2e Programming Manual page 194

NAP - BASIC Stamp Command Reference
the actual timing to vary by as much as –50, +100 percent (i.e., a Period of 0,
NAP can range from 9 to 36 ms). At room temperature with a fresh
battery or other stable power supply, variations in the length of a NAP
will be less than ±10 percent.
One great use for NAP is in a battery-powered application where at least
some small amount of time is spent doing nothing. For example, you may
have a program that loops endlessly, performing some task, and pausing
for approximately 100 ms each time through the loop. You could replace
your PAUSE 100 with NAP 3, as long as the timing of the 100 ms pause
was not critical. The NAP 3 would effectively pause your program for
about 144 ms and, at the same time, would place the BASIC Stamp in low-
power mode, which would extend your battery life.
If your application is driving loads (sourcing or sinking current through
output-high or output-low pins) during a NAP, current will be interrupted
for about 18 ms when the BASIC Stamp wakes up. The reason is that the
watchdog-timer reset that awakens the BASIC Stamp also causes all of the
pins to switch to input mode for approximately 18 ms.
interpreter firmware regains control of the processor, it restores the I/O
direction dictated by your program.
If you plan to use END, NAP, or SLEEP in your programs, make sure that
your loads can tolerate these power outages. The simplest solution is
often to connect resistors high or low (to +5V or ground) as appropriate to
ensure a continuing supply of current during the reset glitch.
The demo program can be used to demonstrate the effects of the NAP
glitch with an LED and resistor as shown in Figure 5.16.
Page 192 • BASIC Stamp Programming Manual 2.0b • www.parallaxinc.com
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