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PBASIC is amicrocontroller-based version ofBASIC created byParallax, Inc. in 1992.[1]
PBASIC was created to bring ease of use to the microcontroller andembedded processor world. It is used for writing code for theBASIC Stamp microcontrollers. After the code is written, it is tokenized and loaded into anEEPROM on the microcontroller. Thesetokens are fetched by the microcontroller and used to generateinstructions for the processor.
When starting a PBASIC file, the programmer defines the version of theBASIC Stamp and the version of PBASIC that will be used. Variables and constants are usually declared first thing in a program. The DO LOOP, FOR NEXT loop, IF and ENDIF, and some standard BASIC commands are part of the language, but many commands like PULSOUT, HIGH, LOW, DEBUG, and FREQOUT are native to PBASIC and are used for special purposes that are not available in traditional BASIC (such as having the Basic Stamp ring apiezoelectric speaker, for example).
In the Stamp Editor, the PBASICintegrated development environment (IDE) running on a (Windows) PC, the programmer has to select 1 of 7 different basic stamps, BS1, BS2, BS2E, BS2SX, BS2P, BS2PE, and BS2PX, which is done by using one of these commands:
' {$STAMP BS1}' {$STAMP BS2}' {$STAMP BS2e}' {$STAMP BS2sx}' {$STAMP BS2p}' {$STAMP BS2pe}' {$STAMP BS2px}The programmer must also select which PBASIC version to use, which he or she may express with commands such as these:
' {$PBASIC 1.0} ' use version 1.0 syntax (BS1 only)' {$PBASIC 2.0} ' use version 2.0 syntax' {$PBASIC 2.5} ' use version 2.5 syntaxAn example of a program using HIGH and LOW to make anLED blink, along with a DO...LOOP would be:
DO HIGH 1 'turn LED onI/O pin 1 on PAUSE 1000 'keep it on for 1 second LOW 1 'turn it off PAUSE 500 'keep it off for 500 msecLOOP 'repeat forever
An example of a program using HIGH and LOW along with the FOR NEXT loop would be:
counter VAR Byte 'sets variable "counter FOR counter = 1 to 5 HIGH 1 'make pin 1logic level high (5 V) PAUSE 1000 'keep it on for 1000 msec LOW 1 'turn it off PAUSE 500 'keep it off for 500 msecNEXT 'redirects to beginning four more timesEND 'end program
Comments in the code are preceded by anapostrophe ('). The microcontroller ignores the rest of the line and continues to the next each time it encounters a comment. PBASIC codes can be simply a list of statements:
HIGH1'turn on LED on pin 1PAUSE1000'pause for one secondLOW1'turn off LED on pin 1END'end program
If the programmer selects 'Run' from the IDE's menu, the program is tokenized anduploaded to the Basic Stamp through an RS232 or USB cable and stored in the stamp's EEPROM asHuffman compressed non-byte-aligned variable-length tokens, and immediately executed.[2] For example, a GOSUB statement uses 20 bits, including 11 bit-oriented addressing bits for the subroutine address. Because statements are non-byte-aligned, a subroutine can start on any bit in any byte in the EEPROM.[3]
ThePICAXE microcontroller uses a version of Basic similar to the version used to program the Basic Stamp I.
