BASIC stamp manual v2.2

CONFIGPIN – BASIC Stamp Command Reference

Page 144 • BASIC Stamp Syntax and Reference Manual 2.2 • www.parallax.com

Every high bit (1) in the PinMask argument enables the output direction

for the corresponding I/O pin while every low bit (0) disables the output

direction. In the above example, I/O pins 8, 4, 1, and 0 are set to the

output direction and all other I/O pins are set to the input direction. This

is similar to the following statement:

DIRS = %0000000100010011

Pull-up resistors are commonly used in circuitry where a component, such

as a button, provides an open/drain signal; the signal is either floating

(open) or is driven to ground (drain). Since the BASIC Stamp input pins

must always be connected to either 5 volts or ground (0 volts) in order to

read a reliable logic state with them, a pull-up resistor is required on

circuitry, such as the button circuit mentioned above, so that the signal is

never left floating (electrically disconnected).

The following example enables internal pull-up resistors on I/O pins 15,

12, 6, and 3, and disables internal pull-up resistors on all other I/O pins:

CONFIGPIN PULLUP, %1001000001001000

Note that the internal pull-up resistors are intentionally weak, about 20

k. Additionally, the internal pull-up resistors can be activated for all

pins, regardless of pin direction, but really matter only when the

associated pin is set to input mode.

An input pin’s logic threshold determines the voltage levels that are

interpreted as logic high (1) and logic low (0). Most microcontrollers, and

other integrated circuits use one of two types of logic threshold: TTL Level

or CMOS Level. The BASIC Stamp I/O pins are, by default, configured

for TTL level logic thresholds. Figure 5.2 is an illustration of the difference

between TTL and CMOS logic levels.

TTL Logic Level CMOS Logic Level

Figure 5.2: TTL and CMOS Logic

Level Threshold Voltages

ULL-UP RESISTORS.

OGIC THRESHOLD.