BASIC Stamp FAQ

STAMP FAQS PROGRAMMING INFORMATION
Last Revised On: 7/21/00 Page: 9
How many I/O pins does the BASIC Stamp have?
The BASIC Stamp I has 8 I/O pins while the BASIC Stamp II, BASIC STAMP IIe and BASIC Stamp IIsx has
16 I/O pins plus 2 special serial port pins (1 input, 1 output).
What can I use the I/O pins for?
The BASIC Stamp’s I/O pins are perfectly suited for digital input and output with TTL/CMOS level (0 to 5 volt)
signals. However, you can use some special commands and techniques to input and output limited analog signals.
For example, the RCTIME and PWM commands can be used to read a variable resistance or output a variable
voltage from 0 to 5 volts. The I/O pins can not be used to read analog voltages by themselves, however, but this
can be done by interfacing the I/O pins to an A to D converter chip.
Can the I/O pins be used to control relays, solenoids and other similar devices?
Yes, however, due to the demanding current and voltage requirements of some of these components, driver circuitry
will need to be used to properly isolate the I/O pins from harmful effects. For examples of this, refer to BASIC
Stamp I Application Note #6 and BASIC Stamp Article #6, “Silicon Steroids for Stamps”.
Can I control LEDs with the I/O pins?
Yes. Simply use a 470 ohm resister in series with the LED to limit the current draw through the I/O pin (see “How
much current can the I/O pins handle?”). Also, keep in mind that most LEDs require a lot of current in relation to
what the BASIC Stamp can provide. If you attach and power 3 or more LEDs at one time from the BASIC
Stamp’s I/O pins, you are likely to see flaky and unpredictable results caused by voltage sag, I/O pin damage
and/or hardware resets. Driver circuitry or low current LEDs will need to be used if you require such an application.
How much current can the I/O pins handle?
On the BASIC Stamp I and BASIC Stamp II, each I/O pin is capable of sourcing 20 mA and sinking 25 mA. The
total across all I/O pins should not exceed 40 mA source or 50 mA sink at any given time, however. One
exception to this rule exists with the BS2-IC. If the BS2-IC is powered by an external 5-volt regulator capable of
delivering at least 100 mA, the total across each group of 8 I/O pins (0 - 7 and 8 - 15) can reach 40 mA source or
50 mA sink providing a total of 80 mA source or 100 mA sink overall. The BASIC Stamp IIsx’s I/O pins can
source and sink 30 mA, and the total across all I/O pins should not exceed 150 mA.
What is the input impedance of the BASIC Stamp’s I/O pins?
Approximately 1 Meg Ohm.
How fast does the BASIC Stamp execute its PBASIC code?
On average, the BASIC Stamp I executes 2000 instructions per second, the BASIC Stamp II executes 4000
instructions per second, the BASIC Stamp IIe executes apx 3800 instructions per second and the BASIC Stamp
IIsx executes 10000 instructions per second. This is only an estimate as the true execution speed depends upon
many factors including, the particular set of instructions used and the type of arguments provided to the instructions.
Some instructions execute at a much faster rate while others, especially those that have to deal with external signal
measurement or specific protocol speeds, will execute much slower.