PIC Architecture
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Lecture 21 -PIC Architecture
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PIC Architecture
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Will now look at another architecture
Look at the microcontroller company
Step 1 – The programmers model
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Philosophy of PIC Architecture
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Embedded processing is pervasive
Electronic intelligence in is everyday products
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Company Philosophy
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Have products that fit the problem
Many systems can be automated using 8-bit
microcontrollers
Much of product line is 8-bit
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Reasons for pervasiveness?
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Competitive pressure
Expanded functionality of products
Provide differentiation in product from that of
competitor
Cost competitive integrated solution
Allow creation of new classes of products
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Microcontroller Solution
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Microcontroller features
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CPU – processing unit
Non-volatile program memory
Re-settable non-volatile data memory
(EEPROM)
RAM for data storage
Direct support for various input/output
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Some typical applications
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Automotive air bag systems
Remote control
Handheld tools
Appliances – coffee pot, mixer, stove, refrigerator,
dish washer, washer, dryer
Major home systems – heating and cooling
Cordless phones and cell phones
Security systems
TV, DVD player/recorder, DVR, PVR
Sound system
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Come in 4-bit through 32-bit
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4-bit
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8-bit
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Still very cheap – often ~$1.00 per chip
16 and 32 bit
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Very inexpensive
Priced at $6.00 to 12.00 each
Evaluation of requirements, chip capability,
and cost come into design decision
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Typical automotive use
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Engine control – 32-bit microcontroller
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Transmission control –16-bit microcontroller
Audio system – 16-bit
Antilock braking – 16-bit
Up to fifty 8-bit microcontrollers for functions of
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Fuel flow, fuel mixture, valve timing, throttle body
opening, spark timing
Wiper control
Electric Mirrors
Air Bags
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Automotive today continued
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Up to fifty 8-bit microcontrollers for functions of
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Wiper control
Electric Mirrors
Air Bags
Fuel pump
Speedometer
Security system
Climate control system
Power windows …..
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Microchip’s position
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Microchip and microcontroller use
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Microcontroller choice parameters
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Number of I/O pins
Amount of program and data memory
Speed
Timer Resources
Interrupt control
Robustness
Error recovery – watchdog timers
Power, I/O expansion, math support
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Block Diagram
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PIC architecture is a “Harvard”
architecture
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The Harvard Architecture
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Feature of Harvard architecture
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Near all instructions are single instruction
word instructions
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Instruction fetch and execute are pipelined so
you can operate at near clock rate instructions
per second
2 separate buses
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Only one fetch per instruction
One for instructions and one for data
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PIC Instruction pipelining
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What % of
time does 1st
flow of
execution
occur??
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Frequency of Branches
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On architectures such as the HP during the
normal flow of a program’s execution on 8 to
12 instructions are executed before a branch
occurs.
(aside) Modern architectures can easily
achieve above 90% correct branch prediction.
This can be factored into actual “speed” of the
processor.
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