Microcontrollers

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Microcontrollers

• InstructorShuvra Das
• mechanical engineering department
• University of Detroit Mercy

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Flowchart of Mechatronic Systems
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Microprocessor Structure

• CPU (Central Processing Units) to recognize and
  carry out program instructions
• Memory storage of data
• I/O Devices to handle communications between the
  computer and outside world
• Busesdigital signals move from one part of the
  computer to another along buses. These could be
  track on a printed circuit board or wires in a
  ribbon cable (e.g.data bus, control bus, address
  bus).

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CPU

• Consists of control unit, arithmetic/logic unit
  (ALU), and various registers.
• The control unit manages the flow and
  manipulation of data. Determines timing and
  sequence of operations.
• A clock circuit provides synchronization
• The ALU performs all arithmetic and logical
  computations on the data that have been
  transferred to appropriate registers.

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Registers

• Accumulator Temporary data storage. To read
  data the CPU needs to address the specific memory
  word.
• E.g. when operating with two numbers only one is
  fetched at one time and stored in the
  accumulator. When the ALU operation is done the
  result is sent back to the accumulator.
• Accumulator Is involved in all data transfers.

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Registers

• Status register contains the status information
  about the latest operations. Usually a bit is
  associated with it and it is called a flag.
• E.g. binary addition 101110 (1) 011 (leads to
  overflow and carries a 1 to the overflow) this
  will raise a flag.
• Program counter register, Memory address
  register, Instruction Register, General-purpose
  register, Stack pointer register.
• The total number and types of registers depends
  on the microprocessor.

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Memory

• Used for storing program, binary data,
  intermediate results from computations.
• Memory units consist of cells that can store
  values 0 or 1. Storage cells are grouped together
  to store one word.
• With a 4-bit address we can access 16 different
  memory units (with each perhaps holding 8 bits)
• Size of a memory unit is specified in terms of
  the number of storage locations available 1K is
  2101024.

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RAM

• Random access memory (RAM) is an example of
  volatile memory information stored in volatile
  memory is lost when power is disconnected.
• In most cases, user programs can read from and
  write to RAM.
• Temporary data is stored in RAM.

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Memory

• ROM (read only memory) cannot be written to by a
  user program. ROM is often used to store look-up
  tables, and program code that will no longer be
  changed (such as operating systems)
• PROM, EPROM, EAROM, EEROM are variations on this,
  which allow ROM to be programmed, and
  reprogrammed.
• Most ROM's are programmed in such a way that the
  data they store are not lost when power is
  disconnected, so ROM is an example of
  non-volatile memory.

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Memory

• EPROM Erasable, Programmable ROM. The
  information is permanently stored by applying a
  voltage to the Integrated circuit. Ultraviolet
  light shined on the quartz window erases this
  memory.
• EEPROM Electrically erasable PROM, erasing
  happens through the application of an electric
  voltage.

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I/O Devices

• Without input and output devices, the
  computational power of a digital computer has no
  meaningful contribution to automation and
  control.
• Disk drives, monitors, and printers are examples
  of output devices. Keyboards, disk drives, and
  scanners are examples of input devices.

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Bus

• These are the paths that data follow throughout
  the computer system.
• Data need to be retrieved from memory into
  registers in the CPU, and the results of
  computation need to be transferred back to
  memory.
• These data transfers take place along the
  bi-directional data bus.
• The parallel and serial ports on a microcomputer
  are other examples of buses.

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Bus

• The address bus carries the address of the memory
  location of data or a program instruction that
  has been requested by the control unit.
• When a particular address is selected in the
  address bus only that location is open to the
  CPU. The CPU can only communicate with one
  location at one time.

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Bus

• Many devices can use a single bus hence it is
  important that the control unit keep track of
  which device is requesting use of the bus, and
  whether it is to receive or send data.

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Bus

• Data bus is used to transport a word from CPU and
  memory or I/O. Word lengths used may be 4, 8,
  16, 32, or 64.
• An 8-bit data bus may consist of 8 separate
  copper tracks laid out on a printed circuit
  board, or it may connect to other devices through
  ribbon cables
• Each wire carries a 0 or 1 signal
• 8 bit microprocessors are very commonly used as
  microcontrollers.
• For 8 bit processor the maximum number of values
  that can be transported is 28256

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Bus

• Control bus is the means by which signals are
  sent to synchronize the separate elements. The
  system clock signals are carried by the control
  bus. These signals generate time intervals
  during which system operations can take place.
  The CPU can send control signals to other
  elements to indicate the type of operation being
  performed
• e.g. whether it needs to READ (receive) and WRITE
  (send) a signal.

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Microcontrollers
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Basic StampII
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Basic Stamp II processorA. BS2 Hardware

• The brain of the BS2 is a custom PIC16C57
  microcontroller, which has been permanently
  programmed with the PBASIC2 instructions set.
• When you run a program on BS2 it retrieves the
  information from a separate memory chip and
  interprets them and carries out the instruction.
• PIC executes 5 million ins/sec. But PBASIC2 does
  3k-4k ins./sec.

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Basic Stamp II processorA. BS2 Hardware

• 20 I/O pins, 16 are for general use, 2 can be
  used for serial communication, 2 are dedicated to
  interfacing with the memory chip.
• P0-P15 interface with 5-volt logic (HIGH5V,
  LOW0V).
• In input mode, the state (1 or 0) of the pin as
  determined by external circuitry can be read. In
  output mode, the pin is internally connected to
  either ground or 5V, depending on the
  programmer's preference.

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A. BS2 Hardware

• BS2 has 32 bytes of RAM (random access memory).
• Six bytes are reserved for input, output and
  direction control of the I/O pins, which leaves
  26 bytes for storing variables.

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Memory chip

• EEPROM- Used for program storage non-volatile
  memory. Not lost due to power loss.
• Can be written to and read from by program, but
  need to keep in mind that there is a limit to the
  number of times you can write to the EEPROM
  (about 10 million).
• Also it takes a long time (as much as several
  millisecond) to write data to memory.

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Reset circuit

• When power is interrupted or corrupted, the reset
  circuit shuts down the BS2 to prevent mistakes or
  lockup, either of which may be dangerous if using
  the BS2 to control heavy equipment.
• When the voltage supply stabilizes, the program
  starts again at the beginning.

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Power supply

• Voltage regulator accepts 5-15V and provides a
  constant 5V. Also allows for low-power modes
  (Sleep, End, Nap instructions).
• Power supply can provide up to 50mA, BS2 needs
  8mA when active. This means that some external
  circuitry can be driven without needing a
  separate supply. (Vdd 5V, Vss ground)

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B. Input/Output, Variables

• RAM has 6 bytes (1 byte 8 bits), reserved for
  managing the I/O pins.
• The remaining 26 bytes are available for
  assigning variables. Fixed variables reside in a
  particular memory location. You are advised to
  use variables which are automatically allocated
  by PBASIC2.
• Variables can be declared as bit, nib (nibble 4
  bits), byte (8 bits), word (16 bits).

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B. Input/Output, Variables

• Declaring as bit means the variable can take on
  values of 0 or 1.
• If declared as nib, the value can be in the range
  from 0 to 15. Byte variables can range from 0 to
  255 and word variables from 0 to 65535.
• In general, use the smallest size that will
  adequately represent the value you need (due to
  26-byte limit on memory.) (Arrays can also be
  declared, but are not discussed here.)

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B. Input/Output, Variables

• Variable modifiers allow us to look at certain
  bits of a variable. For example, RESULT.LOWBIT
  refers to the least significant bit of the
  variable RESULT. Other modifiers include,
  lowbyte, highbyte, nib0, nib1, bit0, bit15, etc
• You can declare constants in PBASIC2. For
  example, if we wish the baud rate of the serial
  output to always be 9600, we may wish to store
  9600 as a constant named BAUD. We need only
  change it in the declaration line.

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Serial host interface

• This interface used for downloading program from
  a host PC (BS2 has no keyboard - programming
  happens on PC, then is downloaded to the EEPROM,
  via serial cable from the PC's serial port to the
  9-pin connector on STAMP2 carrier board.

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Commonly used commands in BS2 programming
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Debug

• Allows you to display variable, constants, or
  expression values while program is running in
  order to follow program flow (debugging).
• Example
• 
  
• 
  X 75
• 
  DEBUG X
• Displays x 75 on the screen.

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End

• End the program, placing the BASIC Stamp into low
  power mode indefinitely.

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GOSUB

• Syntax GOSUB ltSubroutineNamegt
• Make the execution of the program jump to the
  point of the subroutine specified by the
  subroutine name, after storing the address of the
  instruction next to GOSUB. The execution comes
  back to the instruction next to the GOSUB after
  finishing the subroutine by the RETURN
  instruction.
• Example
• GOSUB MyRoutine
• .
• Myroutine
• ---------
• -----------
• RETURN

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RETURN

• Syntax RETURN
• Return the execution from a subroutine to the
  statement following the call of the subroutine of
  this RETURN.

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PULSOUT

• Syntax PULSOUT ltPingt, ltPeriodgt
• Generate a pulse on Pin with a width of Period.
• In BS2 PULSOUT works on units of 2 micro seconds.
• Example
• PULSOUT 12, 750
• Generates a 150 micro second pulse width on pin
  12

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PAUSE

• Syntax PAUSE ltPeriodgt
• Pause the program, execution stops for the
  specified period.

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Number System

• Decimal System 1,2,3,4,5,.
• 103,102,101,100
• thousands,hundreds,tens,units
• Binary system 0,1
• 23,22,21,20
• bit3,bit2,bit1,bit0 (bitsbinary digits)

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Binary Math

• 000
• 01101
• 1110, I.e.,0carry 1
• 111 11, I.e. 1carry 1
• 141933
• 0111010111100001

• 0-00
• 1-01
• 1-10
• 0-110-1borrow 1borrow
• 27-1413
• 11011-0111001101

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C. BS2 Runtime Math and Logic - pay attention!!

• Number Representations BS2 recognizes decimal
  (no prefix), hex ( prefix), binary ( prefix),
  ASCII (string enclosed in quote - example "A"
  returns the ASCII code for A 65.)
• Order of operations BS2 performs operations in
  the order written - big difference from letting
  multiplication and division take priority over
  addition and subtraction.

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C. BS2 Runtime Math and Logic - pay attention!!

• Example 1232/4 doesn't result in 13.5, which
  is what we get if we follow the rules we were
  taught. Rather, BS2 does 1235, then 15230,
  then 30/47. (Note BS2 does integer math, so
  30/4 is 7 not 7.5.) Parentheses are necessary to
  force the multiplication and division to take
  place first.

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C. BS2 Runtime Math and Logic - pay attention!!

• Integer math BS2 uses rules of positive integer
  math. It handles only whole numbers and drops
  fractional parts of any computations. Careful
  with negative numbers - these are stored as 2's
  complement. Better to avoid negative numbers
  when possible. Division with negative numbers
  will not work, but addition, subtraction and
  multiplication are ok, if you are careful. (Also
  use MIN and MAX only with unsigned integers.)

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C. BS2 Runtime Math and Logic - pay attention!!

• Unary and binary operators Unary operators take
  precedence over binary operators 10 - SQR 16
  results in SQR 16 being evaluated first, then
  subtracts it from 10.
• 16-bit workspace Computation is done in 16 bits.
  If variable is byte, it is padded with 8 leading
  zeros to make the operand 16 bits. After the
  operation, the 8 LSB bits are placed into the
  byte variable in which we want to store the
  result. Careful when working with negative
  numbers.

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C. BS2 Runtime Math and Logic - pay attention!!

• Example x -99, where x has been declared as a
  byte. When we ask for the value stored in x to
  be displayed in signed decimal format (PBASIC2
  instruction is "debug sdec ? x"), it shows that x
  is 157. What happened? Note that 99 is 01100011
  as a byte. When BS2 negates 99, it converts the
  number to 16 bits (0000000001100011), then takes
  two's complement (1111111110011101).

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C. BS2 Runtime Math and Logic - pay attention!!

• Since we asked for the value to be stored as x
  (byte), the 8 leftmost bits are truncated, and we
  have (10011101). The SDEC modifier of the debug
  instruction expects the operand to be a 16-bit,
  2-'s complement number, but we are only giving it
  a byte to work with. So it just pads the number
  with leading zeros (0000000010011101), which is
  157.

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FOR NEXT

• Syntax FOR counter ltstartvaluegt TO ltEndValuegt
  STEP ltStepValuegt NEXT
• Create a repeating loop that executes the lines
  between FOR and NEXT, incrementing or
  decrementing the counter according to the step
  value.
• If start value is larger than end value, PBASIC
  understands that the step value is negative even
  if there is no minus sign.

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FORNEXT

• Note For Loops can not overlapped, Example
• FOR I 1 TO 10
• FOR J 1 TO I
• ..
• NEXT
• NEXT

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IFTHEN

• Syntax IF ltconditiongt THEN lttrue-addressgt
• If the condition is true the execution jumps to
  the true-address, otherwise it continues down.

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High

• Syntax High Pin
• Makes the specific pin output high.

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LOW

• Syntax LOW ltPingt
• Make the specific pin output low

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Frequently used PBASIC Instructions

• Debug
• End
• For/Next
• Gosub
• Goto
• High
• IfThen
• Input
• Low

• Output
• Pause
• PWM
• Rctime
• Return
• Serin
• Serout
• Stop
• Toggle

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BRANCH

• Syntax BRANCH offset, (Add0, Add1, , AddN)
• Go to the address specified by offset.
• It works the same way like (switch-case) in C.
• We will use it on look up tables when we have
  more than one table to see which table we are
  going to read.
• If offset 0 gt branch to address add0
• If offset 1 gt branch to address add1
• etc

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DATA

• Syntax ltsymbolgt DATA ltDataItem, DataItem,gt
• Write data to the EEPROM during the program
  download.
• Symbol is an optional, unique symbol that will
  be automatically defined as a constant equal to
  the location number(address) of the first Item.
• DataItem is a constant indicates a value.

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GOTO

• Syntax GOTO label
• Makes the execution jump to the point of the
  program specified by the label.
• A common use on endless loops.
• Example
• loop .
• GOTO loop

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INPUT

• Syntax INPUT ltPingt
• Make the specific pin an input.

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LOOKUP

• Syntax index, (value0, value1, valueN),
  variable
• Find the value at location index and store it in
  variable
• If index 0 gt variable value0
• Else if index 1 gt variable value1
• etc

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OUTPUT

• Syntax OUTPUT ltPingt
• Make the specified pin an output.

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PWM

• Syntax PWM ltPingt, ltDutygt, ltCyclesgt
• Convert a digital value to analog output via
  pulse-width modulation.
• Units in cycles on BS2 is 1 ms.
• Average voltage equation V(avg) (Duty/255) 5
  Volts.
• Required charge time(cycles) equation t(chg) 4
  R C
• Example
• T(chg) 4 1000 10-6 40 ms
• So PWM 0, 100, 40
• Will Put a 1.96 V charge on the capacitor

1000 ohm
P0
Vo
0.1 uF
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RCTIME

• Syntax RCTIME ltPingt, ltStategt, ltVariablegt
• Measure time while Pin remains in State and put
  the result on Variable usually to measure the
  charge/ discharge time of resistor/ capacitor
  (RC) circuit.
• We will use that on our following light program,
  by comparing the RCTIME of the left and the right
  photo sensors (resistor on our case) and use the
  comparison result to decide whether we we should
  turn right or left.

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READ

• Syntax READ ltLocationgt, ltVariablegt
• Read value at Location and store the result in
  Variable.
• Usually used on lookup tables.

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SERIN

• Receive asynchronous serial data (e.g, RS-232
  serial protocol data).
• We are not going to use serial communication
  interface on our project(s).
• For details refer to the user manual.

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SEROUT

• Transmit asynchronous serial data (e.g RS-232
  data).
• Again we are not dealing with serial
  communication interface.

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STOP

• Syntax STOP
• Stop program execution without putting BASIC
  stamp into low-power mode, also you can use it in
  the middle of the program (differences from END).
• Use this command on error handling (ex divide by
  zero), or if your program branches based on the
  inputs into more than one independent algorithm,
  so each algorithm considered as separated program
  has to end when finished.

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TOGGLE

• Syntax Toggle ltPingt
• Invert the state of an output pin, if it is high
  make it low and vice versa.

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Sample Programs