1. BASIC Stamp II Programming for Descartes Robots
Alexander Stoytchev
Mobile Robot Laboratory
Georgia Tech
CS4630: Robotics and Sensing

2. Descartes Robot

3. Bumpers

4. Motors

5. Wheel Encoders

6. Wheel Belts

7. Serial Cable

8. System Requirements IBM PC or compatible computer
3.5" floppy disk drive
serial port
128K of RAM
MS-DOS 2.0 or higher.
A color video display is recommended.

9. Onboard Computer

10. Microcontroller Layout

11. BASIC Stamp II Manufactured by Parallax Inc.
Runs Parallax BASIC (PBASIC) programs.

12. BASIC Stamp II Processor: Parallax PIC16C57 EEPROM: 2048 bytes
RAM: 16 word registers (or 32 bytes!!!)
Max. Program Length: ~500 instructions
Clock Speed: 20-MHz
Execution Speed: 4000 instructions/sec.
Current Requirements: 7 mA running, 50 uA in sleep modes
16 I/O Lines;
RS-232 input & output ( K bauds)
Price $49

13. Secondary Processor Microchip(TM) PIC16C71 RISC, 10MHz
Automatically executes commands received from the main processor without intervention
Motor PWM pulsing for speed control
encoder monitoring for wheel position and velocity
A/D conversions
navigation control
monitoring tasks

14. Electrical Diagram

15. EEPROM Layout

16. RAM Layout

17. PBASIC Parallax BASIC Token interpreter in program memory of the PIC
EEPROM as token and data memory

18. Types WORD, BYTE, NIB, BIT VAR, CON, DATA symbol VAR type
symbol VAR size(array)
symbol VAR variable.modifier
symbol CON expression
symbol DATA type
symbol DATA data, data, ...

20. Operators

21. Common Arithmetic Problems
Evaluation is always from left to right
X = 2 + 3* ‘= 20
X = 3* ‘= 14
X = 2 + (3*4) ‘= 14

22. IF IF variable ?? value {AND/OR variable ?? value ...} THEN address
?? can be =, <>, =>, =<, >, <
Variable(s) will be compared to Value(s).
Value is a variable/constant.
Address is a label which specifies where to go if condition is true.

23. BRANCH BRANCH offset,(address0,address1...addressN)
Branch to address specified by offset (if in range).
Offset is a variable/constant which specifies which Address# to use (0-N).
Addresses are labels which specify where to go.

24. Jumps & Subroutines
GOTO label
GOSUB subname
RETURN

25. FOR Loop
FOR variable = start TO end {STEP {-}increment} NEXT {variable}
Variable will be used as a counter
Start is the initial value of Variable
End is the terminal value of Variable
Increment is an optional value which overrides the default counter delta of +1.
If Increment is negative it is subtracted

26. EEPROM Symbol DATA data, data, … READ location,variable
WRITE location,data
EEPROM {location},(data,data...)
Preload EEPROM data locations (those not used by the program).

27. DEBUG DEBUG cls,"Text",cr,var,$var,%var,#var,#$var,#%var
Display information in the debug window
Text to be printed can be expressed in quotes;
cls - clear screen
cr - carriage return
Simply naming the variables prints their current values
Decimal is the default,
$ - can be used for hex
% - can be used for binary.
# - (with optional '$' or '%' in front) the variable name will not be printed, instead only the value will be printed.

28. Unary Operators

29. Sin(x) Example y=sin(x) , x= 0 to 2*Pi
Y= 127 * sin (X/256 *2*Pi), X=1 to 255
The whole circle is described by 256 steps

30. Sin(x) and Cos(x)

31. Pausing and Sleeping STOP - like end but no power consumption
PAUSE milliseconds
NAP period
Power consumption is reduced to an extent dependent upon the length of the period.
duration 2^period * ~18ms. Period (0 to 7)
SLEEP seconds
resolution is ~2.3s, accuracy is ~99.9%
Power consumption reduced to 1/100th normal
Seconds is a variable/constant ( ).
STOP - like end but no power consumption
END
Sleep terminally until the power cycles (program re-runs) or the pc connects.
Power is reduced to an absolute minimum

32. Miscellaneous SERIN pin,baudmode,(qualifier,qualifier...)
RANDOM wordvariable
SOUND pin#,(note0, duration0, note1, duration1, ….)
SERIN pin,baudmode,(qualifier,qualifier...)
SEROUT pin,baudmode,({#}data,{#}data...)

33. Robot Commands: Initialization
The secondary PIC communicates with the BS2-IC at 50kbps over a serial link.
Port 15 is used for communication.
Port 14 is used for flow control.
The PIC requires about 80ms to start-up.
PAUSE use before every program
SEROUT 15\14, 0, ["I"] - to reset the PIC

34. Syntax of PIC Commands
SEROUT 15\14, 0, ["C", VALUE.LOWBYTE, VALUE.HIGHBYTE]
C is the command character (not case-sensitive).
VALUE.LOWBYTE is the low byte of the value.
VALUE.HIGHBYTE is the high byte of the value.

35. Going Forward and Backward
SEROUT 15\14, 0, ["F", 100]
SEROUT 15\14, 0, ["B", 44, 1]
DISTANCE VAR WORD
DISTANCE = 300
SEROUT 15\14, 0, [“B", DISTANCE.LOWBYTE, DISTANCE.HIGHBYTE]

36. Requesting Sensor Data
Send a SEROUT request for data followed IMMEDIATELY by a SERIN command.
‘Read left wheel encoder counts
DISTANCE VAR WORD
DL VAR DISTANCE.LOWBYTE
DH VAR DISTANCE.HIGHBYTE
SEROUT 15\14, 0, ["["]
SERIN 15\14, 0, [DL, DH]

37. Heading Information SEROUT 15\14, 0, ["?"] SERIN 15\14, 0, [HEADING]
HEADING should be (turn resolution = 2 degrees)
HEADING VAR WORD
HEADING = 320
SEROUT 15\14, 0, ["H", HEADING/2]
HEADING = HEADING * 2

38. Making Turns SEROUT 15\14, 0, [“L“, 20] ‘ turn left 40 degrees
SEROUT 15\14, 0, [“R“, 30] ‘ turn right 60 degrees
Turn parameter * 2 = turn angle
SEROUT 15\14, 0, [“H“, 45] ‘ Set heading
SEROUT 15\14, 0, [“T“, 45] ‘ Set target heading

39. Motor Control SEROUT 15\14, 0, [“M“, %1010]
%00 turn off motor
%01 set in backward motion
%10 set in forward motion
SEROUT 15\14, 0, [“S“, 10] ‘ Set Speed
Valid speeds Automatic speed compensation.
SEROUT 15\14, 0, [“<“, 10] ‘ Set left motor speed
SEROUT 15\14, 0, [“>“, 15] ‘ Set right motor speed
SEROUT 15\14, 0, [“(“] ‘ Request left wheel instantaneous velocity
SEROUT 15\14, 0, [“)“] ‘ Request right wheel instantaneous velocity
SEROUT 15\14, 0, [“#“] ‘ Request Stopped State
SEROUT 15\14, 0, [“C“] ‘ Clear distances traveled

40. Common Problems “Hardware Not found” error message
Check Serial cable orientation
Power down and up
Check arithmetic operations for overflows
Variable names and values

41. References http://www.divent.com http://www.parallaxinc.com/
File: progrmng.html
Claus Kuhnel and Klaus Zahnert “BASIC Stamp” (second edition), Newness, 2000