BasicStamp II Language Quick Tutorial

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BasicStamp II Language(Quick) Tutorial
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Lexical Aspects

• Line oriented language (one stmt per line)
• Multiple statements separated by
• Lines limited to 256 chars, extended with
  trailing _
• Each line may have a label at start (label)
• Comments start with single quote ' (to EOL)
• Identifiers like other languages
• Including underscore
• Not case sensitive

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Lexical Aspects

• Literals
• Decimal 123
• Hex FF
• Binary 10101110
• Chars A
• Strings string
• Only useful in parameters to certain built in
  statements
• Means s, t, r, i, n, g

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Variables

• Flat global name space
• Variable declaration
• var
• bit nib byte word (nibnibble4 bits)
• 1, 4, 8, 16 bits values
• E.g., counter var byte
• Arrays
• var ()
• e.g., table var byte(5)

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Variables (cont.)

• Aliases (two names for the same variable)
• var
• var .
• bit0 bit1 bit2 bit15
• highbit lowbit
• nib0 nib3 highnib lownib
• byte0 byte1 highbyte lowbyte
• Example LED_pin var outs.bit5

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Constants

• Declaration
• con
• Limits on
• Evaluated left to right, no parens
• Example sw_time con 41 1

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Expressions

• 8 and 16 bit unsigned integers
• Operators
• -/ (all as in C or Java)
• top 16 bits of multiplication
• / mult top 8 as in, low 8 as fraction
• // remainder (mod)
• Evaluated left-to-right (wrong precedence!)
• Parens allowed to change order of eval

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More Operators

• ABS absolute value
• MIN, MAX min and max (5 MIN 3)
• SQR integer square root
• SIN, COS sine cosine
• Input 0..255 for 0..360deg
• Output 127127

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More Operators

• DCD decode creates bit mask w/ 1 bit set
• (DCD 2) 00000100 bits numbered 0..7
• NCD encode find highest bit set
• (NCD 01001000) 7 bits numbered 1..8 (!)
  
• (NCD 00000000) 0
• REV reverse some low order bits
• (10101000 REV 4) 10100001

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Comparison and Logical Operators

• The usual comparison operators
• Logical operators
• not and or xor
• Zero is false, non-zero is true

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Assignment Conditionals

• ()
• .
• If Then

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Control Statements

• For To Step
  
• Next
• Note always executes at least once through loop!
• Goto
• Branch , ,
• Labels numbered from 0
• If index is larger than label set no jump is made

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Control Statements (cont.)

• Gosub
• call basic subroutine at label (ending at return)
• no parameters
• Return
• return from most recently called subroutine

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Control Statements (cont.)

• End
• stop execution and enter low power mode
• I/O pins retain state
• Stop
• stop execution but dont enter low power mode
• I/O pins retain state
• Control starts at the first statement in your
  code
• It is possible to run off the bottom of your
  program (apparently starts back at the top??)

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Placing Data in EEPROM Memory

• Non-volatile memory
• keeps values w/o power
• Data , ,
• Data , ,
• Fill EEPROM with values
• Optionally defining constant to starting address
• Values are placed at program download time not
  run-time

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Placing Data in EEPROM Memory

• Read ,
• Write ,
• Read / write a value from / to given EEPROM
  address

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Sleeping and Low Power Mode

• PIC has low power mode (draws 1?A)
• Typical low power strategy sleep most of the
  time
• Sleep
• Nap
• Timing is not extremely accurate

• NAP Codes
• 0 18msec
• 36msec
• 72msec
• 144msec
• 288msec
• 576msec
• 1.152sec
• 2.304sec

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Accurate Delays (Full Power)

• Pause
• Do nothing for given number of milliseconds
• Example pause 500 ½ second delay

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Misc. Statements

• Lookup ,, ,
• Table lookup for 8 or 16 bit values
• Constant from Nth position (from 0) goes in
• Strings count as multiple single character
  entries
• Out of range index causes no action

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Misc. Statements

• Lookdown , ,
• Search for a value in an 8-bit constant table
• Strings equivalent to list of single characters
• Var gets index of matching value (0 based
  indexing)
• If not found then no action taken
• Lookdown , ,
• First that given comparison succeeds
• Random
• Generate 16-bit random number using var as seed
  (and result)

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I/O Related Statements

• Both low level , simple functions
• Input, Output, High, Low
• And high level, complex functions
• I2Cin, SerIn, etc.

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Statements for Low Level I/O

• Input , Output
• Establish direction of single pin
• Reverse
• Reverse direction of a single pin
• High , Low
• Implies output (most I/O commands imply
  input/output)
• Same as Output
• Toggle
• Invert value of pin
• To read input value

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Additional I/O

• Button , , , , ,
  ,
• Wait for debounced repeated button
  press/release on pin
• Have a look at the manual

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Additional I/O

• Pulsein , ,
• Measure width of high/low pulse on pin
• 0 low pulse, 1 high pulse
• Returns in units of 2?sec (0 for too long /
  never)
• Pulseout ,
• Emit measured pulse in units of 2?sec
• High/low depends on prior state (toggles pin
  twice)
• Count , ,
• Count pulses occurring within given time (in
  msec)

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Analog I/O

• RCTime , ,
• Measure time pin stays in current state
• 2?sec units
• Typical use charge pin then measure time it takes
  RC circuit to drain
• See example from last slides

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Analog and Audio I/O

• PWM , ,
• Pulse width modulation output on pin
• PWM signal is used to efficiently drive e.g., DC
  motor at fractional speed
• High only some percentage (duty cycle)
• 0 0 on, 255 100 on
• Delivers of full power
• note not clean square wave
• in msec units

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Analog and Audio I/O

• FreqOut , ,
• FreqOut , , ,
• Output sine wave(s) at given frequency
• Use filter capacitors for reasonable sound

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Analog and Audio I/O

• DTMFOut , , ,
• DTMFOut , , , , ,
• Output telephone touch tones (DTMF)
• Generated with FreqOut
• Needs low pass filter (freqout)
• Values 0..15
• 10 is
• 11 is
• 12..15 are defined, but not on the phone

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Serial I/O

• Shiftin
• , , , ,
  \,
• Shiftout , , , ,
  \,
• Serin , , ,
• Serout , , ,
• items can be qualified with formatting
  information
• e.g. dec for ascii decimal encoding
• Also can do flow control and timeouts (see
  manual)
• Debug , ,

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About Serial Output

• RS232C is standard for serial communications
• EIA recommended standard from the early 60s
• Designed for modems
• Uses odd voltages (from modern perspective)
• Logical 1 (mark) 15..-3v
• Logical 0 (space) 3..15v
• Stamps can put out 0 and 5v. so we have a
  problem

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Level conversion for RS232

• Maxim makes a single chip (powered by only 5v)
• Built into BS II (used for Debug only)
• Can buy HW that fits inside connector case (15)
• http//www.sxlist.com/techref/io/serial/RCL1.htm

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Or you can cheat for about .04

• It turns out that most PC serial ports have a
  wide margin of things they will accept
• If you invert the signal (1 0v 0 5v) it
  turns out that most PC serial ports will accept
  it as RS232!
• Special modes for Serin (e.g., N9600) to do this
• PICs have over/under voltage protection on pins
• Negative voltage clamped and read as logic 0
• Voltage 5V also clamped and read as 1
• Because of details, need current limiting
  resistors in series

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Serial cheater cable

• Has worked on all (both) PCs Ive tried
• Failed on 1 Mac I tried

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Debugging Strategies

• When programming you dont really spend your
  time/effort writing code, you spend it debugging
  the code when you get it wrong (which is pretty
  much always)
• Embedded systems are particularly hard
• Is it hardware or software?
• Impoverished debug environment
• Few tools
• Low visibility
• Timing may be an issue

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Software Debugging in PBP

• Have the equivalent of printf (debug)
• If you have the code space
• And you are not timing dependent
• Can get small serial driven LCD displays
• Can also do things like flash LED on Pin
• E.g., unique patterns indicating that certain
  pieces of code are being executed

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Hardware debugging

• Preemptive debugging (AKA testing)
• Seriously test your circuits before you use them
• Start with ensuring power doesnt conduct to
  ground
• Check that connections actually conduct
• Check that adjacent soldered holes arent shorted
• Multimeter for basic continuity checks
• Double check that you have connected everything
• Double check that you have connected it right
• Polarity, etc.
• Check that you have power (battery ok)

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Hardware debugging

• Logic probe
• Very useful to checking that basic signals you
  expect are showing up on the pin you expect
• Clipped to power and ground, needle touches
  point to probe
• Indicates 0/1
• Also shows fast pulses long enough to see

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Hardware Debugging

• Oscilloscope
• Shows graph of actual voltages over time

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Hardware Debugging

• Can scale time (horiz) or voltage (vert)
• Can typically trigger
• Start graph at point of some event
• E.g., first rise
• Graph allows time measurements
• E.g., see at right that pulse lasts just under
  1msec
• Some allow dual trace
• Allows comparisons

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