The Basic Stamp

1
The Basic Stamp

• Instruction Set Architecture

2
The Microprocessor

• A microprocessor is a computer that typically has
  an architecture that is well suited to embedded
  systems applications
• Built in memory
• Built in I/O pins and registers
• Hardware interface support
• The instruction set is typically of the Reduced
  Instruction Set Computer (RISC) type
• A minimalist list of instructions required to
  manipulate hardware devices
• Nothing fancy
• They are usually rolled out as a family of
  devices
• Various capabilities to suite a multitude of
  embedded applications
• Were using the BASIC Stamp BS2
• The microprocessor is a PIC16C57
• There are a family of BASIC Stamp processors
  including BS1, BS2, BS2E, BS2SX, BS2P, BS2PE,
  BS2PX

3
The BS2 Instruction Set

• While most microprocessor instruction sets are
  specified in Register Transfer Language (RTL) and
  assembly language, the BS2 is specified in PBASIC
• The architecture is specifically designed to
  execute PBASIC instructions

4
Preliminaries

• The BASIC Stamp IDE is designed to work with the
  entire family of BASIC Stamp devices
• Thus, it is important that you provide the
  correct compiler directives in your code
• 'STAMP BS2 'STAMP directive (specifies a BS2)
• 'PBASIC 2.5 ' PBASIC Version directive
• The IDE has buttons to insert these into your
  code (you dont have to memorize them)

5
The Instructions
6
Branching

• GOSUB address
• Jump to subroutine, address (label)
• ON offset GOSUB address1, address2, address3,
• Call the subroutine at the 0-based offset in the
  address label list
• RETURN
• Return from a GOSUB or ON GOSUB command
• GOTO address
• Jump to a specific address (label)
• ON offset GOTO address1, address2, address3,
• Jump to the 0-based offset in the address label
  list

7
Looping

• DO
• statements
• LOOP
• DO WHILE (condition)
• statements
• LOOP
• DO UNTIL (condition)
• statements
• LOOP
• DO
• statements
• LOOP WHILE (condition)
• DO
• statements
• LOOP UNTIL (condition)

• FOR counter start TO end STEP value
• statements
• NEXT
• Beware of counting down, strange things may
  happen due to 2s complement notation
• EXIT
• Bail out of a loop early (like break in Java)

8
Conditional Branching

• IF condition THEN address
• Goto address label if condition is true
• IF condition THEN
• statements
• ELSEIF condition THEN
• statements
• ELSE
• statements
• ENDIF
• Conditional statement, ELSEIF is optional
• BRANCH value, case0, case1, case2
• Equivalent to
• IF value 0 THEN case0
• IF value 1 THEN case1
• IF value 2 THEN case2
• SELECTCASE

9
Data Declarations RAM

• symbol VAR type
• Type can be
• Bit 1 bit
• Nib 4 bits
• Byte 8 bits
• Word 16 bits
• Arrays
• symbol VAR type(entries)
• Alias
• symbol VAR symbol
• Partial access though suffixes
• .BITn
• .NIBn
• .BYTEn
• .LOWBYTE
• .HIGHBYTE

10
Data Declarations EEPROM

• DATA value1, value2, value3,
• Write data values to EEPROM to be read later with
  READ
• Differs from VAR in that DATA uses EEPROM and VAR
  uses RAM
• READ location, variable
• read a value from the EEPROM that was previously
  loaded with a DATA command
• WRITE location, data
• write data to address location in the EEPROM

11
Data access

• LOOKDOWN value, item0, item1, item2, result
• Assign the 0-based index of value in the item
  list into result
• No assignment if value is not in the item list
• LOOKUP index, value0, value1, value2, result
• Assign the value from item list at 0-based index
  into result
• No assignment if index is too big

12
Termination

• END
• End the program, go to low power mode
• STOP
• Stop program execution without going into low
  power mode

13
Power Management

• NAP period
• go to reduced power mode for 2period 18 mSecs
• SLEEP duration
• put the BASIC stamp into low power mode for
  duration Seconds rounded up to units of 2.3
  seconds
• PAUSE duration
• Sleep for duration mSecs (stay in normal power)

14
Input/Output

• BUTTON pin, downstate, delay, rate, workspace,
  targetstate, address
• Read button state with debounce options
• COUNT pin, duration, variable
• Count the number of 0-1-0 or 1-0-1 transition for
  duration time in mSec
• HIGH pin
• Set a high signal on pin
• LOW pin
• Set a high signal on pin

15
Input/Output

• INn
• Read from pin n
• OUTn
• Write to pin n
• TOGGLE pin
• Invert the state of the pin

16
Input/Output

• FREQOUT pin, duration, frequency
• Output a sine wave on a pin
• PWM pin, duty, duration
• Use pulse-width modulation to convert a digital
  value to analog
• PULSIN pin, state, variable
• Measure the width of an incoming pulse on the
  specified pin
• PULSOUT pin, duration
• Send a pulse to pin of width duration in units of
  2 uSecs

17
Input/Output

• SERIN
• Read RS232 formatted data on an I/O pin
• SEROUT
• Write RS232 formatted data on an I/O pin

18
Miscellaneous

• Math
• SIN, COS, ABS, SQR, RANDOM
• Note that these do not return floating point
  numbers
• The return integers within some defined range
• DEBUG output, output,
• Write data to the debug monitor window

19
And Then Some

• There are many more commands
• Ive just touched on the most useful ones for
  what we do
• Online help installed with the IDE shows all
• Look for those labeled BS2
• Full manual can be gotten here
• http//www.parallax.com/dl/docs/prod/stamps/web-BS
  M-v2.2.pdf