BasicStamp II Language(Quick) Tutorial
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
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”
Variables • Flat global name space • Variable declaration: <name>var<type> <type>: bitnibbyte word (nib=nibble=4 bits) • 1, 4, 8, 16 bits values • E.g., counter var byte • Arrays <name>var<type>(<size>) e.g., table var byte(5)
Variables (cont.) • Aliases (two names for the same variable) <name1>var<name2> <name1>var<name2>.<part> <part>: bit0 bit1 bit2 … bit15 highbit lowbit nib0 … nib3 highnib lownib byte0 byte1 highbyte lowbyte • Example: LED_pin var outs.bit5
Constants • Declaration <name>con<constant expr> • Limits on <constant expr> • Evaluated left to right, no parens Example: sw_time con 41 + 1
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
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: –127…127
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
Comparison and Logical Operators • The usual comparison operators = <>< > <= >= • Logical operators: not and or xor • Zero is false, non-zero is true
Assignment & Conditionals <name> = <expr> <name>(<expr>)= <expr> <name>.<part> = <expr> If <expr> Then <label>
Control Statements For <var> = <expr> To <expr> Step <val><stmt-list> Next Note: always executes at least once through loop! Goto <label> Branch <expr>, [<label>, …] • Labels numbered from 0 • If index is larger than label set no jump is made
Control Statements (cont.) Gosub<label> • call basic subroutine at label (ending at return) • no parameters Return • return from most recently called subroutine
Control Statements (cont.) End • stop execution and enter low power mode • I/O pins retain state Stop • stop execution but don’t 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??)
Placing Data in EEPROM Memory • Non-volatile memory • keeps values w/o power • Data <const>, <const>, … • <constname> Data <const>, <const>, … • Fill EEPROM with values • Optionally defining constant to starting address • Values are placed at program download time not run-time
Placing Data in EEPROM Memory Read <addr>,<var> Write <addr>,<val> • Read / write a value from / to given EEPROM address
Sleeping and Low Power Mode • PIC has low power mode (draws ~1A) • Typical low power strategy: sleep most of the time Sleep<seconds> Nap<code> • Timing is not extremely accurate • NAP Codes • 0 18msec • 36msec • 72msec • 144msec • 288msec • 576msec • 1.152sec • 2.304sec
Accurate Delays (Full Power) Pause <msec> • Do nothing for given number of milliseconds • Example: pause 500 ‘ ½ second delay
Misc. Statements Lookup<index>,[<const>, …],<var> • Table lookup for 8 or 16 bit values • Constant from Nth position (from 0) goes in <var> • Strings count as multiple single character entries • Out of range index causes no action
Misc. Statements Lookdown<val> [<const>, …],<var> • 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<val> <compop> [<const>, …],<var> • First that given comparison succeeds • = <> < > <= >= Random <var> • Generate 16-bit random number using var as seed (and result)
I/O Related Statements • Both low level , simple functions • Input, Output, High, Low • And high level, complex functions • I2Cin, SerIn, etc.
Statements for Low Level I/O Input <pin>, Output <pin> • Establish direction of single pin Reverse<pin> • Reverse direction of a single pin High<pin>, Low<pin> • Implies output (most I/O commands imply input/output) • Same as “Output<pin>:<pin>=<val>” Toggle<pin> • Invert value of pin <var>=<pin> • To read input value
Additional I/O Button<pin>, <down>, <delay>, <rate>, <bvar>, <action>, <label> • Wait for debounced & repeated button press/release on pin • Have a look at the manual…
Additional I/O Pulsein <pin>, <state>, <var> • Measure width of high/low pulse on pin • <state> = 0 low pulse, = 1 high pulse • Returns in units of 2sec (0 for too long / never) Pulseout <pin>, <time> • Emit measured pulse in units of 2sec • High/low depends on prior state (toggles pin twice) Count <pin>, <time>, <var> • Count pulses occurring within given time (in msec)
Analog I/O • RCTime<pin>, <state>, <var> • Measure time pin stays in current state • 2sec units • Typical use charge pin then measure time it takes RC circuit to drain • See example from last slides
Analog and Audio I/O • PWM<pin>, <duty>, <time> • 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) • <duty> 0 = 0% on, 255 = 100% on • Delivers % of full power • note: not clean square wave • <time> in msec units
Analog and Audio I/O • FreqOut<pin>, <on_msec>, <freq1> • FreqOut<pin>, <on_msec>, <freq1>, <freq2> • Output sine wave(s) at given frequency • Use filter capacitors for reasonable sound
Analog and Audio I/O • DTMFOut<pin>, [ <v1>, <v2>, …] • DTMFOut<pin>, <onms>, <offms>, [ <v1>, <v2>, …] • 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
Serial I/O Shiftin <datapin>, <clkpin>, <mode>,[<var>, <var>\<bits>, …] Shiftout<datapin>, <clkpin>, <mode>,[<var>, <var>\<bits>, …] Serin<pin>, <mode>, [ <item>, …] Serout <pin>, <mode>, <item>, … • items can be qualified with formatting information • e.g. “dec” for ascii decimal encoding • Also can do flow control and timeouts (see manual) Debug <item>, <item>, …
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
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
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
Serial “cheater” cable • Has worked on all (both) PCs I’ve tried • Failed on 1 Mac I tried
Debugging Strategies • When programming you don’t 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
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
Hardware debugging • “Preemptive debugging” (AKA testing) • Seriously test your circuits before you use them • Start with ensuring power doesn’t conduct to ground • Check that connections actually conduct • Check that adjacent soldered holes aren’t 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)
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
Hardware Debugging • Oscilloscope • Shows graph of actual voltages over time
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
