Microcontroler Overview Lecture Notes

What is a Microcontroller?

• Small, lightweight CPU

• Some Families:
• PIC
• SH1
• ADuC812
• 68HC11
• Allows:
• Simple hardware to software interface
• In situ processing (on a PCB, shoe, etc)
• Less ICs (no more digital logic chips)
• Has limited:
• Speed, usually < 5 MIPS
• RAM, ~ 256 bytes
• Program storage, 4K instructions
• Basic Features
• I/O Pins
• Usually digital, some analog (see later)
• Timers
• 8 or 16 bit
• Watchdog (resets/wakes up processor after timeout)
• x Bit operations
• Usually 8, makes 16 (and greater) bit operations slow
• External Addressing
• Gives ability to add extra RAM

• Hardware UART
• Allows for serial line communications
• Can be mimicked in software, but:
• Slower
• Uses a timer
• Cannot trigger interrupt

• ADC/DAC
• Analog to Digital / Digital to Analog Conversion
• Usually 8 bit (up to 16 bits)
• Usually 20us per sample (down to 5)
• Can be multiplexed (4051) for more inputs

• Interrupts
• Allow asynchronous program flow based on external events
• Based on:
• Pin change
• Serial event
• Power low (etc)
• Can wake processor
• Hard to debug
• Flash Programmable
• As opposed to UV erasable (which takes ~15 min)
• Faster prototyping
• Sometimes not available with ADC
• CISC vs. RISC
• CISC
• Different instruction sizes and execution times
• Easier to write assembly language by hand
• RISC
• All instructions same size and (almost) same execution time
• Compiler can usually create smaller code
• Much easier cycle counting

Some processor families: (Click on name for block diagram)

• PIC  (www.microchip.com)
• Usually:
• 18 - 28 pin packages (down to 8) with 14-22 I/O
• ADC available, usually 4 channels, 8 bits
• Max. 5 MIPS
• Hardware UART on heavier chips
• No external addressing
• Excellent general purpose chips
• Ubiquitous around the Lab
• SH1 7032 (eg of Hitachi SH family) (semiconductor.hitachi.com/superh/)
• Lots of:
• Speed (20 MIPS)
• Bits (32)
• RAM (8K)
• 16 bit timers (5)
• Interrupts (40)
• Power drain (100 mA)
• Pins to solder (100)

 
• ADuC812 (www.analog.com/industry/microconverter)
• Fast (5 us) 8 channel, 12 bit ADC
• Hardware UART
• Flash
• But:
• CISC
• 1.25 MIPS max
• Still good for data collection, smart sensor type application

• 68HC11 (http://ebus.mot-sps.com/ProdCat/sg/0,1251,98635,00.html)
• 8 channel, 8 bit ADC
• 20K program, 1K RAM
• 5 16-bit timers
• 38 I/O pins
• UART
• 24 bit external memory space
• But: 3 MHz clock
• See also 68HC12/68HC16