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 • We’re 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 don’t 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 2’s 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 SELECT…CASE • compact form of an IF THEN ELSEIF command

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 .LOWNIB .HIGHNIB

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 • I’ve 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-BSM-v2.2.pdf