Parallax BASIC Stamp 2e, Programming Manual

Page: 88 / 353

BUTTON - BASIC Stamp Command Reference
Page 86
•
BASIC Stamp Programming Manual 2.0b
•
www.parallaxinc.com
demonstration of switch bounce, see the demo program for the Count
instruction.)
BUTTON also lets PBASIC react to a button press the way your computer
keyboard does to a key press. When you press a key, a character
immediately appears on the screen. If you hold the key down, there’s a
delay, then a rapid-fire stream of characters appears on the screen.
BUTTON’s auto-repeat function can be set up to work much the same
way.
BUTTON is designed for use inside a program loop. Each time through
the loop, BUTTON checks the state of the specified pin. When it first
matches DownState, BUTTON debounces the switch. Then, in accordance
with TargetState, it either branches to address (TargetState = 1) or doesn’t
(TargetState = 0).
If the switch stays in DownState, BUTTON counts the number of program
loops that execute. When this count equals Delay, BUTTON once again
triggers the action specified by TargetState and address. Hereafter, if the
switch remains in DownState, BUTTON waits Rate number of cycles
between actions. The Workspace variable is used by BUTTON to keep
track of how many cycles have occurred since the pin switched to
TargetState or since the last auto-repeat.
BUTTON does not stop program execution. In order for its delay and auto
repeat functions to work properly, BUTTON must be executed from
within a program loop.
Figure 5.1: Sample BUTTON
circuits. Active-high (left) and
active-low (right).
to I/O pin
PB Switch
10 k
Ω
Vdd
Vss
active-high
(downstate = 1)
to I/O pin
PB Switch
10 k
Ω
Vdd
Vss
active-low
(downstate = 0)