Many type of sketches are able to run on the Teensy! The digitial I/O pins work with digitialWrite(pin,value), digitalRead(pin), and pinMode(pin,mode). The PWM pins can be used with analogWrite(pin,value). Eight (8) pins can be used as interrupts with attachInterrupt(). The Teensy++ has 8 analog inputs that can be used with analogRead().

Communication can be done using Serial.print() and other communication functions normally used for communication on the Arduino board. Unlike the Arduino, which converts 38.4 kbps serial to USB, the Teensy has direct 12 MBit/sec USB access, so communications are sent and received at full USB speed.

Direct USB access is possible, so the Teensy is not limited to being only a serial-type USB device. It can act as HID, Mass Storage, or nearly any type of USB device. Future Teensyduino releases will provide alternate board configurations that act as non-serial devices.

The Teensy also has a serial port. It is not connected the USB port and can be used separately.

How Does Teensy Compare With The Arduino Board?

Specification	Teensy	Teensy++	Arduino
Processor	AT90USB162	AT90USB646	ATMEGA168
Flash Memory	15872	64512	14336
RAM Memory	512	4096	1024
EEPROM Memory	512	2048	512
Digital I/O	21	38	14
Analog Inputs	0	8	6
PWM (Analog Out)	4	9	6
USB Port	1	1	(serial only)
Serial Port	1	1	1
I2C (TWI) Port	0	1	1
Clock Speed	16 MHz	16 MHz	16 MHz

Teensy uses a similar Atmel AVR processor as the Arduino board, but there are differences. The most important is direct, built-in USB on the Teensy compared to serial converted to USB by a separate chip on the Arduino. While this allows much faster communication, and also many types of USB communication that are impossible with a standard Arduino, it is also a very different from a technical point of view! Some sketches may depend on the serial-based behavior in subtle ways, and thus may not work properly on a Teensy with direct USB.

Teensyduino attempts to make Teensy as compatible with sketches as possible. If you discover a bug or compatability problem, please report it to paul@pjrc.com.

The Teensy lacks analog inputs. Sketches that require analog input can not work on the Teensy. The Teensy also has less RAM and fewer PWM capable pins than an Arduino. Teensy is designed for easy use on breadboards in the smallest possible size, which is incompatible with the form-factor used by Arduino shields.

While many types of sketches can run, Teensy is NOT an "Arduino clone" due to the substantial technical differences. The Teensy hardware and Teensyduino software add-on are NOT endorsed or supported by the Arduino developer team.