Motorola M68HC11

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Motorola M68HC11

• Motorola offers two basic 8-bit families of
  microcontrollers, the 68HC05 being the
  inexpensive core and the 68HC11 the higher
  performance code.
• The Motorola M68HC11 family, based on the
  Motorola 6800 microprocessor, is very widely used
  for control systems. There are number of
  versions, the differences being due to
  differences in the ROM, RAM, EPROM, EEPROM and
  configuration register features.

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Motorola M68HC11 ..

• For example, 68HC11A8 has 8K ROM, 512 bytes
  EPROM, 256 bytes RAM, 16-bit timer system, a
  synchronous serial communication interface, an
  8-channel 8-bit analog-to-digital converter for
  analogue inputs, ad five ports A, B, C, D and E.

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Block Diagram of M68HC11
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Motorola M68HC11 ..

• Input/Output ports
• Port A may be used as an 8-bit input/output port
  or for timer or pulse accumulator function. It is
  controlled by two registers the port A data
  register PORTA at address 1000 and the pulse
  accumulator control register PACTL at address
  1026
• Port B is output only. Its data register is at
  the address 1004 and to output data it has to be
  written to this memory location

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Motorola M68HC11 ..

• Port C can be either input or output, data being
  written or read from its data register at address
  1003. Its direction is controlled by the port
  data direction register ad address 1007. The
  eight bits in this register correspond to the
  individual bits in port C and determine whether
  the lines are inputs or outputs when the
  corresponding data direction register bit is set
  to 0 it is an input and when set to 1 an output.

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Motorola M68HC11 ..

• Port D contain just six lines, either input or
  output, and it has a data register at address
  1008 the directions are controlled by a port
  data direction register at address 1009.
• Port D also serves as the connection to the two
  serial subsystems of the microcontroller. The
  serial communication interface (SCI), controlled
  by a register at 102D, is an asynchronous system
  which provides serial communication that is
  compatible with modems and terminal. The Serial
  peripheral Interface is controlled by a register
  at 1028

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Motorola M68HC11 ..

• Port E is an 8-bit input only port, data register
  at 100A, which can be used as a general-purpose
  input port or for analogue inputs to the internal
  analog-to-digital converter
• The A/D converter has two lines VRH and VLH
  provides the reference voltages used by the ADC
  the high reference voltage should not lower than
  VDD, i.e. 5V and the low reference should not
  lower than VSS, i.e. 0V.

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Motorola M68HC11 ..

• The oscillator system pins XTAL and EXTAL are the
  connections needed to access the internal
  oscillator. E is an output from the bus clock and
  runs at one-quarter of the oscillator frequency
  and can be used to synchronize external events.
• Interrupt Controller is to enable interruptions
  of a program. The two lines IRQ and XIRQ are for
  inputs of the interrupt signal. RESET is for
  resetting. An interrupt is an event that requires
  the CPU to stop normal program execution and
  perform some service related to the event.

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Motorola M68HC11 ..

• Timer
• The microcontroller has three timers timer 0,
  timer 1, and timer 2. Timer 0 is an 8-bit counter
  which can be written to or read from and can be
  used to count external signal transitions,
  generating an interrupt when the required number
  of events have occurred. The source of the count
  can be either the internal bus clock signal or an
  external digital signal.

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Motorola M68HC11 ..

• COP
• The computer operating properly function. This
  is a timer which times out and resets the system
  if an operation is not concluded in what is
  deemed a reasonable time. This is often termed
  watchdog timer because it is watching for
  unreasonable delays which might occur as a result
  of a fault in the system.

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Motorola M68HC11 ..

• PWM
• Pulse width modulation is used to control the
  speed of dc motor. A square wave signal is
  generated and the amount of time for which the
  signal is high is controlled. As a consequence
  the average value of the signal is controlled,
  hence the voltage supplied to the motor is also
  controlled.