Microcontrollers

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Microcontrollers

• CPU
• Memory
• I/O capabilities
• Specialized peripherals
• M68HC11
• Descended from Motorola 6800 processor
• Still active product, but not recommended for new
  designs
• http//www.freescale.com/webapp/sps/site/taxonomy.
  jsp?nodeId01624684498635

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M68HC11 A and E Families
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M68HC11 Block Diagram
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M68HC11E

• CPU
• Memory
• RAM
• ROM
• EEPROM
• I/O
• Timer(s)
• Serial I/O
• A/D Converter

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Multimode Pins

• Many pins have multiple names
• Pins can be connected internally to two or more
  functions
• Use of some feature may preclude use of another
• Example
• PA7/PAI/OC1
• PA7 bidirectional I/O pin
• PAI pulse accumulator input
• OC1 Output compare 1
• Pins usage depends on operating mode or register
  settings

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68HC11 Processor Mode

• Determined at reset
• State of MODB and MODA pins
• Latched state can be read from HPRIO register
  (0x103C)

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Single Chip Mode

• Stand-alone microcontroller mode
• Code is executed from internal ROM/EPROM
• Reset and interrupt vectors are at 0xFFCO
  0xFFFF
• All I/O port are available
• Multimode pin restrictions still apply

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Expanded Multiplexed Mode

• Configured with an external address and data bus
  to interface to addition memory and peripherals
• Sacrifice two I/O ports (B and C)
• Address bus 16 bits 216 addresses
• Data bus 8 bits

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Expanded Mode Connections
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Test Mode

• Special mode for prototyping and testing
• Less-restrictive expanded bus mode
• Reset and interrupt vectors mode to EEPROM at
  0xBFC0 0xBFF0

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Bootstrap Mode

• Special mode
• Less-restrictive single chip mode
• Activate a small internal ROM at 0xBF40 0xBFFF
• Contains a program which will download a small
  program into internal RAM via serial link (SCI)
• Will then execute downloaded program

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Memory Maps
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Mode Selection

• Varies by need
• Embedded Systems
• Select normal mode (single-chip or expanded)
• Perhaps use special mode to start and switch to a
  normal mode early
• Development Systems
• Use a special mode for flexibility
• Interrupt vectors in RAM
• Can change some registers that cannot normally be
  changed
• Boot-loader mode can be useful

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HPRIO Register

• SMOD Reflects inverse of MODB input pin at
  reset
• May be cleared by software control from a special
  mode, changing the mode, but never set.
• MDA Status of MODA pin at reset
• May be written when SMOD is set (special mode)

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Other Config Registers

• INIT
• Remap internal memory
• May only be done once and within 64 cycles of
  reset
• OPTION
• Turn on I/O subsystems

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Homework

• What mode(s) is the Handy Board capable of
  operating in?
• What mode(s) will we likely use? Why?
• Due Thursday at beginning of lecture.