PBASIC is a microcontroller-based version of BASIC created by Parallax, Inc. in 1992. PBASIC was created to bring ease of use to the microcontroller and embedded processor world. It is used for writing code for the BASIC Stamp microcontrollers. After the code is written, it is tokenized and loaded into an EEPROM on the microcontroller. These tokens are fetched by the microcontroller and used to generate instructions for the processor.
Syntax
When starting a PBASIC file, the programmer defines the version of the BASIC 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.
Programming
In the Stamp Editor, the PBASIC integrated development environment running on a 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:
' ' ' ' ' ' '
The programmer must also select which PBASIC version to use, which he or she may express with commands such as these:
' ' use version 1.0 syntax ' ' use version 2.0 syntax ' ' use version 2.5 syntax
An example of a program using HIGH and LOW to make an LED blink, along with a DO...LOOP would be: DO HIGH 1 'turn LED on I/O pin 1 on PAUSE 1000 'keep it on for 1 second LOW 1 'turn it off PAUSE 500 'keep it off for 500 msec LOOP '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 1 logic level high PAUSE 1000 'keep it on for 1000 msec LOW 1 'turn it off PAUSE 500 'keep it off for 500 msec NEXT 'redirects to beginning four more times END 'end program Comments in the code are preceded by an apostrophe. 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: HIGH 1 'turn on LED on pin 1 PAUSE 1000 'pause for one second LOW 1 'turn off LED on pin 1 END 'end program
If the programmer selects 'Run' from the IDE's menu, the program is tokenized and uploaded to the Basic Stamp through an RS232 or USB cable and stored in the stamp's EEPROM as Huffman compressed non-byte-aligned variable-length tokens, and immediately executed. 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.
Other Chips
The PICAXE microcontroller uses a version of Basic similar to the version used to program the Basic Stamp I.
