Input - Parallax BASIC Stamp 2e Programming Manual

2
1 2
e
1
NOTE: Expressions are not allowed
as arguments on the BS1. The
range of the Pin argument on the
BS1 is 0 – 7.
5: BASIC Stamp Command Reference – INPUT

INPUT

2 2 INPUT Pin
sx p
Function
Make the specified pin an input.
• Pin is a variable/constant/expression (0 – 15) that specifies which
I/O pin to set to input mode.
Explanation
There are several ways to make a pin an input. When a program begins,
all of the BASIC Stamp's pins are inputs. Commands that rely on input
pins, like PULSIN and SERIN, automatically change the specified pin to
input. Writing 0s to particular bits of the variable DIRS makes the
corresponding pins inputs. And then there's the INPUT command.
When a pin is an input, your program can check its state by reading the
corresponding INS variable (PINS on the BS1). For example:
INPUT 4
Hold:
IF IN4 = 0 THEN Hold
The code above will read the state of P4 as set by external circuitry. If
nothing is connected to P4, it will alternate between states (1 or 0)
apparently at random.
What happens if your program writes to the OUTS bit (PINS bit on the
BS1) of a pin that is set up as an input? The value is stored in OUTS (PINS
on the BS1), but has no effect on the outside world. If the pin is changed to
output, the last value written to the corresponding OUTS bit (or PINS bit
on the BS1) will appear on the pin. The demo program shows how this
works.
1 Demo Program (INPUT.bas)
' This program demonstrates how the input/output direction of a pin is determined by
' the corresponding bit of DIRS. It also shows that the state of the pin itself (as
' reflected by the corresponding bit of PINS) is determined by the outside world when
' the pin is an input, and by the corresponding bit of PINS when it's an output. To
' set up the demo, connect a 10k resistor from +5V to P7 on the BASIC Stamp. The
' resistor to +5V puts a high (1) on the pin when it's an input. The BASIC Stamp can
' override this state by writing a low (0) to bit 7 of OUTS and changing the pin to output.
BS1 BS2 BS2e BS2sx BS2p
BASIC Stamp Programming Manual 2.0c • www.parallaxinc.com • Page 155
' Stay here until P4 is 1.