ENGR PBASIC programming

Transcription

1 ENGR 1100 PBASIC programming

2 Variables Why variables? To store values, Why store variables? To count, Why count? To control and keep track of the number of times something happens

3 Variables Variables can be used to store values. Before you can use a variable in PBASIC, you have to declare the variable. variablename VAR Size You can declare four different sizes of variable in PBASIC: Size Stores Bit 0 to 1 Nib 0 to 15 Byte 0 to 255 Word 0 to or to

4 Variable Declaration A variable in PBASIC is declared with the syntax of: variablename VAR size, for example

5 Variables can be read and modified. 'Prog 5B: Test of variable sizes ' *********************** Declare Variables ByteCount VAR BYTE WordCount VAR WORD BitCount VAR BIT NibCount VAR NIB Main: WordCount = WordCount 'Add to each variable ByteCount = ByteCount + 20 NibCount = NibCount + 1 BitCount = BitCount + 1 DEBUG CLS 'Clear the screen DEBUG? WordCount : DEBUG? ByteCount: DEBUG? NibCount: DEBUG? BitCount PAUSE 500 GOTO Main Colons may be used to separate instructions on a single line

6 DEBUG The DEBUG command is used solely for the purpose of observing the execution of a program not able to change values of variables or affect the flow of a program.

7 DEBUG DEBUG text to be displayed Prints the string between the quotes to the debug window. DEBUG dec variable Prints the value of variable to the debug window. DEBUG cr cr is the carriage return parameter. It moves the cursor the next line in the debug window. DEBUG cls Clears the debug window screen.

8 DEBUG example variable VAR byte variable = 27 DEBUG cls, The value of the variable is:, dec variable, cr DEBUG This is the second line. DEBUG Variable =, dec variable

9 DEBUG ' Robotics with the Boe-Bot - TimedMessages.bs2 ' Show how the PAUSE command can be used to display messages at human speeds. ' {$STAMP BS2} ' {$PBASIC 2.5} DEBUG "Start timer..." PAUSE 1000 DEBUG CR, "One second elapsed..." PAUSE 2000 DEBUG CR, "Three seconds elapsed..." DEBUG CR, "Done." END

10 Debug DEBUG "Hello!" DO DEBUG "!" PAUSE 1000 LOOP

11 PAUSE The PAUSE command suspends the execution of a program a specified amount of time.

12 HIGH, LOW Issuing the HIGH command sets the specified pin number to five volts. The LOW commands sets the specified pin number to zero volts.

13 HIGH, LOW HIGH 11 sets pin 11 to five volts LOW 12 sets pin 12 to zero volts

14 Variable Example ' {$STAMP BS2} ' {$PBASIC 2.5} value VAR Word variables anothervalue VAR Word value = 500 variables anothervalue = 2000 DEBUG? value DEBUG? anothervalue value = 10 * anothervalue operations DEBUG? value again DEBUG? anothervalue END ' Declare Initialize ' Display values ' Perform ' Display values

15 FOR..NEXT LOOP The most convenient way to control the number of times a piece of code is executed is with a FOR NEXT loop. Here is the syntax: FOR Counter = StartValue TO EndValue {STEP stepvalue} NEXT ' {$STAMP BS2} ' {$PBASIC 2.5} mycounter VAR Word FOR mycounter = 1 TO 10 DEBUG? mycounter PAUSE 500 NEXT DEBUG CR, "All done!" END

16 Do..LOOP You can place your commands between the words DO and LOOP if you want them executed over and over again. DO LOOP ' Display a message once every second. ' {$STAMP BS2} ' {$PBASIC 2.5} DO DEBUG "Hello!", CR PAUSE 1000 LOOP

17 Do Loop An EXIT command can be issued inside the DO...LOOP command variable VAR byte DO IF variable = 10 THEN EXIT LOOP

18 Pulseout PULSOUT Pin, Duration DO PULSOUT 13, PAUSE 2000 LOOP

19 IF..THEN The IF THEN statement is used to make decisions in PBASIC. The syntax for IF THEN statements is: IF (condition) THEN {ELSEIF (condition)} {ELSE} ENDIF IF (IN7 = 0) THEN HIGH 1 ELSE LOW 1 ENDIF IF (IN5 = 0) THEN HIGH 10 ELSE LOW 10 ENDIF

20 variable VAR word What would this do? IF (variable > 4000) THEN DEBUG Variable was greater than 4000, cr ELSEIF (variable = 4000) THEN DEBUG Variable was equal to 4000, cr ELSE DEBUG Variable was less than 4000, cr ENDIF

21 Blinking an LED with HIGH, LOW Main: HIGH 8 PAUSE 1000 LOW 8 PAUSE 5000 GOTO Main 'Turn off LED 'Wait 1 second 'Turn on LED 'Wait 5 seconds 'Jump back to beginning

22 Subroutine There are two parts of a PBASIC subroutine. Call Actual Subroutine

23 Subroutine It starts with a label that serves as its name and ends with a RETURN command. The commands between the label and the RETURN command is the code block that does the job you want the subroutine to do.

24 Subroutines DO DEBUG "Before subroutine",cr PAUSE 1000 GOSUB My_Subroutine DEBUG "After subroutine", CR PAUSE 1000 LOOP My_Subroutine: DEBUG "Command in subroutine", CR PAUSE 1000 RETURN

25 Subroutines ' Make forward movement in reusable subroutines. ' {$STAMP BS2} ' {$PBASIC 2.5} counter VAR Word GOSUB Forward END Forward: FOR counter = 1 TO 64 PULSOUT 13, 850 PULSOUT 12, 650 PAUSE 20 NEXT PAUSE 200 RETURN