Instructor: Nachiket M' Kharalkar

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Introduction to Microcontrollers

• Instructor Nachiket M. Kharalkar
•  
• Lecture 12
• Date 06/29/2007
• E-mail knachike_at_ece.utexas.edu
•  

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Todays Agenda

• Recap
• Fixed point numbers
• LCD interfacing

LCD slides Courtesy Prof. Bard
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Implementation

• Stack implementation of local variables has four
  stages
• binding
• allocation
• access, and
• deallocation.

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• Example of local variables on stack
• org 4000
• calculate sum of numbers
• Input RegD num
• Output RegD Sum of 1,2,3,...,num
• Errors may overflow
• 1) binding
• num set 2 loop counter 1,2,3
• sum set 0 running
• calc
• 2) allocation
• pshd allocate num
• movw 0,2,-sp sum0
• 3) access
• loop ldd sum,sp
• addd num,sp
• std sum,sp sum sumnum
• ldd num,sp
• subd 1

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Call by reference call by value

• call by reference
• how
• a pointer to the object is passed
• why
• fast for passing lots of data
• simple to implement input/output parameters
• both subroutine and calling routine assess same
  data
• call by value
• how
• a copy of the data is passed
• why
• simple for small numbers of parameters
• protection of the original data from the
  subroutine

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• org 4000
• calculate sum of numbers
• Input RegD num
• Output RegD Sum of 1,2,3,...,num
• Errors may overflow
• 1) binding
• sum set -4 16-bit accumulator
• num set -2 loop counter 1,2,3
• calc
• 2) allocation
• pshx save old frame
• tsx create frame
• pshd allocate num
• movw 0,2,-sp sum0
• 3) access
• Draw a stack picture relative to frame
• X-4 -gt sum
• X-2 -gt num
• X -gt oldX

Example of local variables on stack, using a
stack frame Advantage you can use the stack for
other temporary Disadvantage slower ties up the
use of a register
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Parameters and locals on stack, using a stack
frame

• Advantage you can pass lots of data
• Disadvantage slower
• Strategy
• number of parameters?
• few use registers
• a lot use the stack
• size of the parameter
• 1 or 2 bytes call by value
• buffers call by reference

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Fixed point numbers

• Why
• express values with non-integer values
• no floating point hardware support
• When
• range of values is known
• range of values is small
• How
• 1) variable integer, called I.
• may be signed or unsigned
• may be 8, 16 or 32 bits (precision)
• 2) fixed constant, called ? (resolution)
• value is fixed, and can not be changed
• not stored in memory
• specify this fixed content using comments

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Fixed point numbers

• The value of the fixed-point number
• fixed-point number ? I?
• Decimal fixed-point, ?10m
• decimal fixed-point number I 10m
• nice for human input/output
• Binary fixed-point, ?2m
• binary fixed-point number I 2m
• easier for computers to perform calculations

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?0.01 V Vin 5N/255 how ADC works Vin I
0.01 definition of fixed point I
(5100N)/255 substitution I (100N)/51
simplify I (100N25)/51 round to closest
integer
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Fixed point conversion example

• Consider the following digital filter
  calculation.
• y x -0.0532672x1 x2 0.0506038y1-0.9025y2
• The variables y, y1, y2, x, x1, and x2 are all
• integers
• -0.0532672 -142-8
• 0.0506038 132-8
• -0.9025 -2312-8
• y x x2 (-14x113y1-231y2)gtgt8

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Input/Output Considerations

• Processor-Peripheral Timing Mismatch
• Peripherals, e.g., displays, sensors, switches,
  generally operate MUCH slower than processor
  instruction times
• Processor MHz
• Peripheral KHz or Hz
• MANY instructions can be executed while
  peripheral processes information

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Input/Output Considerations (cont.)

• Peripheral primitive states
• READY
• Peripheral is ready to initiate an I/O transfer
• BUSY
• READY peripheral becomes BUSY when I/O transfer
  initiated
• Peripheral remains BUSY for duration of I/O
  transfer
• Another transfer can NOT be initiated
• NOT READY
• Peripheral is unable to perform I/O transfer

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Input/Output Considerations (cont.)

• I/O options what to do while the peripheral is
  BUSY
• TEST/TRANSFER (aka, ready/busy, gadfly)
• Poll peripheral status wait for READY/NOT BUSY
• Perform other tasks between polls
• Unless timed correctly, under/over run possible
• One solution POLL CONTINUOUSLY

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Input/Output Considerations (cont.)

• I/O options what to do while the peripheral is
  BUSY
• INTERRUPT/TRANSFER
• Hardware INTERRUPTS processor on condition of
  READY/NOT BUSY
• Facilitates performing other background -
  processing between I/O transfers
• Processor informed (changes context) when current
  transfer complete
• Requires program structure to process context
  change

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Input/Output Considerations (cont.)

• Simplified option
• Suppose that a BUSY control signal is not
  available
• Employ Blind Cycle approach
• Perform I/O operation
• Wait for a period of time that is guaranteed to
  be sufficient for operation to complete
• Initiate next operation

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LCD Liquid Crystal DisplayFeatures

• Low power consumption
• Appears to be a capacitor
• Charge changes reflectivity or transmittivity
• Read with ambient light contrast with LEDs
• Flexibility in size and shape
• LCD is a sandwich
• Transparent LCD material Active PCB
• Size and shape determined by PCB
• Contrast with LEDs

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LCD Liquid Crystal DisplayOperation

• MDL(S) 16166 LCD display
• Consider LCD display to be 1 X 16 matrix
• Each of the 16 character positions behaves as a 5
  X 8 matrix
• Any combination of the 40 picture elements
  (pixel) per character position can be activated
• Each of the 16 characters can be considered as an
  independent display COMPLEX!

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LCD Liquid Crystal DisplayOperation (cont.)

• Simplification provided by
• Hitachi HD 44780U (LCD-II) Dot Matrix LCD
  Controller/Driver
• The HD 44780U will serve as an interface between
  the 6812 and the LCD display
• It will serve to generate the appropriate 5 X 8
  bit patterns for the ASCII character set
• It will handle display character positioning,
  e.g., where next characters are added

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LCD Liquid Crystal DisplayOperation (cont.)

• Interface to HD44780
• Employ 4-bit data mode
• Port M0-5
• Character addresses
• Left 00 07
• Right 40 - 47

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LCD Liquid Crystal DisplayAssignment

• Laboratory assignment
• Interface LCD to Tech Arts board
• Develop device driver to serve as interface
  between 6812 and HD 44780
• Develop main program that employs device driver
  to display message, Welcome to 319K on LCD
• Use EspressSCH to develop circuit diagram

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LCD Liquid Crystal DisplayDevice Driver

• A Device Driver is a set of software routines
  that provide the basic I/O functions of a
  peripheral to higher level programs
• Device drivers encapsulate the specific
  operational details of an I/O device and provide
  the I/O function
• For example, the fact that 42 might be required
  to activate a read function on one type of
  network interface while 80 is required on
  another would only be known by the device driver
  and NOT the program using the driver.

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LCD Liquid Crystal DisplayDevice Driver (cont.)

• Device drivers enable
• Simplified installation of new hardware
• Different algorithms to be employed for I/O
  transfers and control
• Error detection
• Changes in protocol timing
• Simplified implementation of higher level
  software systems

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LCD Liquid Crystal DisplayDevice Driver

• LCD Device Driver functions
• LCD_Open
• Initializes timer, port M data direction
• LCD_OutChar
• Transfers one byte as two nibbles to the
  display
• LCD_Clear
• Clears the display and homes the cursor

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LCD Liquid Crystal DisplayDevice Driver (cont.)

• LCD Device Driver functions
• LCD_OutString
• Transfers a null terminated string of characters
  to the display by calling LCD_OutChar
• LCD_GoTo
• Moves the cursor to a particular display address
• LCD_OutDec
• Displays a 16-bit unsigned number in decimal
  format
• LCD_OutFix
• Displays fixed-point numbers with resolution
  0.001 in unsigned decimal format, 0.000 to 9.999

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LCD Liquid Crystal DisplayDevice Driver (cont.)

• Device Driver Private Function
• outCsr transfers one byte of command to the
  display
• Available to the drivers public functions, e.g.,
  LCD_xyz
• Not available to higher level software

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• Entry Mode Set 0,0,0,0,0,1,I/D,S
• I/D1 for increment cursor move direction
• 0 for decrement cursor move direction
• S 1 for display shift
• 0 for no display shift
• Display On/Off Control 0,0,0,0,1,D,C,B
• D 1 for display on
• 0 for display off
• C 1 for cursor on
• 0 for cursor off
• B 1 for blink of cursor position
  character
• 0 for no blink
• Cursor/Display Shift 0,0,0,1,S/C,R/L,,
• S/C1 for display shift
• 0 for cursor movement
• R/L1 for shift to left
• 0 for shift to right
• Function Set 0,0,1,DL,N,F,,
• DL1 for 8 bit

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LCD_Open

• LCD_Open
• 0) save any registers that will be destroyed by
  pushing on the stack
• 1) initialize timer Timer_Init()
• 2) wait 100ms allowing the LCD to power up (can
  skip this step in TExaS)
• 3) set DDRM so that PM5-0 are output signals to
  the LCD
• 4) E0, RS0
• 5) 4-bit DB7,DB6,DB5,DB4 02 (DL0 4-bit mode)
• 6) E1
• 7) E0 (latch 4-bits into LCD)
• 8) blind cycle 90 us wait
• 9) outCsr(06) // I/D1 Increment, S0 no
  displayshift
• 10)outCsr(0C) // D1 displayon, C0 cursoroff,
  B0 blink off
• 11)outCsr(14) // S/C0 cursormove, R/L1
  shiftright
• 12)outCsr(28) // DL0 4bit, N1 2 line, F0 5by7
  dots
• 13)LCD_Clear() // clear display
• 14)restore the registers by pulling off the stack

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LCD_OutChar

• 0) save any registers that will be destroyed by
  pushing on the stack
• 1) E0, RS1
• 2) 4-bit DB7,DB6,DB5,DB4 most significant
  nibble of data
• 3) E1
• 4) E0 (latch 4-bits into LCD)
• 5) 4-bit DB7,DB6,DB5,DB4 least significant
  nibble of data
• 6) E1
• 7) E0 (latch 4-bits into LCD)
• 8) blind cycle 90 us wait
• 9) restore the registers by pulling off the stack

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LCD_Clear, LCD_OutString

• LCD_Clear
• 0) save any registers that will be destroyed by
  pushing on the stack
• 1) outCsr(01) // Clear Display
• 2) blind cycle 1.64ms wait
• 3) outCsr(02) // Cursor to home
• 4) blind cycle 1.64ms wait
• 5) restore the registers by pulling off the stack
• LCD_OutString
• 0) save any registers that will be destroyed by
  pushing on the stack
• 1) read one character from the string
• 2) increment the sting pointer to the next
  character
• 3) break out of loop (go to step 6) if the
  character is NUL(0)
• 4) output the character to the LCD by calling
  LCD_OutChar
• 5) loop back to step 1)
• 6) restore the registers by pulling off the stack

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LCD_GoTo, LCD_OutDec

• 0) save any registers that will be destroyed by
  pushing on the stack
• 1) verify proper values of DDaddr
• 2) outCsr(DDaddr80 11000000 C0)
• 3) restore the registers by pulling off the stack
• LCD_OutDec (recursive implementation)
• 1) allocate local variable n on the stack
• 2) set n with the input parameter passed in RegD
• 3) if(n gt 10)
• LCD_OutDec(n/10)
• n n10
• 4) LCD_OutChar(n30) / n is between 0 and 9 /
• 5) deallocate variable

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OutFix

• Output characters to LCD display in fixed-point
  format
• unsigned decimal, resolution 0.001, range 0.000
  to 9.999
• Inputs RegD is an unsigned 16-bit number
• Outputs none
• Registers modified CCR
• E.g., RegD0, then output ?0.000 ?
• RegD3, then output ?0.003 ?
• RegD89, then output ?0.089 ?
• RegD123, then output ?0.123 ?
• RegD9999, then output ?9.999 ?
• RegDgt9999, then output ?. ?

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outCsr

• sends one command code to the LCD
  control/status
• Input RegA is 8-bit command to execute
• Output none
• 0) save any registers that will be destroyed by
  pushing on the stack
• 1) E0, RS0
• 2) 4-bit DB7,DB6,DB5,DB4 most significant
  nibble of command
• 3) E1
• 4) E0 (latch 4-bits into LCD)
• 5) 4-bit DB7,DB6,DB5,DB4 least significant
  nibble of command
• 6) E1
• 7) E0 (latch 4-bits into LCD)
• 8) blind cycle 90 us wait
• 9) restore the registers by pulling off the stack

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LCD interfacing

• The IO-gtHD44780 command allows you to connect an
  integrated liquid crystal display (LCD)
• PT4 means PT7,PT6,PT5,PT4
• LCD is physically 16 characters in 1 row, but
  internally 8 characters in 2 rows

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Dialog box for interfacing a simple LCD display
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• Entry lds 4000
• cli
• bset ATDDIEN,C0 PAD7, PAD6 digital
• bclr DDRAD,C0 PAD7, PAD6 inputs
• jsr LCD_Open Your function that
  initializes the LCD
• start jsr LCD_Clear Your function that
  clears the display
• ldx Welcome
• jsr LCD_OutString Your function
  that outputs a string
• ldx TestData
• loop brset PTAD,80, wait for switch
  release
• brclr PTAD,80, wait for switch touch
• jsr LCD_Clear Your function that clears
  the display
• ldd 0,x
• jsr LCD_OutDec Your function that
  outputs an integer
• jsr LCD_GoTo Your function that
  moves the cursor
• ldd 2,x
• jsr LCD_OutFix Your function that
  outputs a fixed-point

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LCD demo