9/20/6 Lecture 21 -PIC Architecture 1

PIC Architecture

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PIC Architecture Will now look at another architecture Look at the microcontroller company Step 1 – The programmers model

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Philosophy of PIC Architecture Embedded processing is pervasive Electronic intelligence in is everyday products

Company Philosophy 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? 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 Microcontroller features

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 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 4-bit

Very inexpensive 8-bit

Still very cheap – often ~$1.00 per chip 16 and 32 bit

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 Engine control – 32-bit microcontroller

Fuel flow, fuel mixture, valve timing, throttle body opening, spark timing

Transmission control –16-bit microcontroller Audio system – 16-bit Antilock braking – 16-bit Up to fifty 8-bit microcontrollers for functions of

Wiper control Electric Mirrors Air Bags

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Automotive today continued Up to fifty 8-bit microcontrollers for functions of

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 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 The Harvard Architecture

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Feature of Harvard architecture Near all instructions are single instruction

word instructions Only one fetch per instruction

Instruction fetch and execute are pipelined so you can operate at near clock rate instructions per second

2 separate buses One for instructions and one for data

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PIC Instruction pipelining What % of

time does 1st flow of execution occur??

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Frequency of Branches 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.