1. Choosing a Microcontroller Architecture
Selecting a 16-bit Microcontroller
Feb 21, 2013 Bill Giovino

2. What You Will Learn Today
What exactly is a 16-bit Microcontroller?
Why 16-bit microcontrollers are still going strong
16-bit Peripherals – faster, FASTER!
When you need a 16-bit
Selection Criteria

3. What is a 16-bit Microcontroller?
A 16-bit Microcontroller moves 16-bit data efficiently
Modern 16-bit architecture takes one cycle to move 16-bit data from one location to another
Modern 16-bit architecture takes one cycle to add two 16-bit numbers
…and it takes more than one cycle to do the same with 32-bit data
If it has a 16-bit datapath and a 16-bit ALU
It’s a 16-bit microcontroller
Duh
If it has an 8-bit datapath and a 16-bit ALU
It’s an 8-bit microcontroller
Sometimes called an 8/16-bit microcontroller
If it has a 16-bit datapath and a 32-bit ALU
It’s a 16-bit Microcontroller
Sometimes called a 16/32-bit Microcontroller
Don’t get hung up on what it’s called, it’s what you do with it that counts.

4. Squeezing Between 8-bit and 32-bit
High Performance
Register Based
Higher cost compared to 8-bit
Plenty of Communications stacks
16-bit
Register-based
Good Low Power
32-bit performance excluding math
Plenty of communications stacks
Lots of Communications Interfaces
Ethernet, USB, CAN, etc
8-bit
Low Power
Lowest Cost
Usually Accumulator Based
Moderate Performance
Moderate Communications
Limited performance with 16-bit communications and stacks

5. 16-bit Microcontrollers All About Embedded Communications
Stubborn fan base
TI, Infineon, Renesas with strong 16-bit base
More complex applications than 8-bit, but lower power than 32-bit
Code is easier to write than an accumulator-based 8-bit because 16-bit is register based
More on-chip resources and performance available to do on-chip debugging, run a monitor, set status pins, etc.
Best balance of Low Power vs. Performance
Driven by 1. Networking features Ethernet, USB, etc is all 16-bit 2. Price 3. Low Power (Great tools are assumed)
Features more important than price
A 16-bit core has more attractive ease-of-use for interfacing to networking peripherals than 8-bit

6. Example: 8-bit doing Ethernet
10/100BaseT Ethernet MAC (16-bit data)
Runs O.K. at 10BaseT (10 Mb/s)
Limited performance at 100BaseT (100Mb/s) because:
8-bit core moves 8-bit data
Meanwhile, Ethernet peripheral is 16-bit data register
8-bit core is moving 16-bit data, which requires an EXTRA read, an EXTRA write – which slows the performance of the core down by as much as one-half
Running at a faster clock speed increases power consumption
Best compromise for low power is a 16-bit microcontroller

7. Popular 16-bit Microcontrollers This list is not complete – so don’t flame me
TI MSP430 – The Dominator
Very Long history, Register based, Low Power
Hugely loyal fan base
Extremely popular
Renesas M16C
Long History, Register Based, Low Power
Code compatible with the popular Renesas 8-bit R8C
Infineon C166 & XC166 – The Boxers
Register based, NOT Low-Power
Lots of Flash
Plenty of performance that competes easily with Cortex
“More than 500 Million pieces sold”
Microchip PIC24 – New Kid on the Block
Register based, Very Low Power
Wide selection in a short period of time
Focused on embedded communications
Freescale S12 – The Company Previously Known As Motorola
Born of the aged 68HC11, Accumulator based, Low Power
Popular 16-bit in Automotive

8. LOW POWER COMMUNICATIONS The Sweet Spot of the 16-bit Market
16-bit is the minimum core architecture size for effective networking
Low Power 16-bit targets battery powered communications
If battery powered, Low Power provides: Longer Battery Life
Whether battery powered or not, Low Power always provides:
Less Power => Less expensive voltage regulator
Less Current => less Expensive PC board layout
Less Heat => Increased MTBF
Less Heat => Reduced cooling requirements (cheaper case design)
Low Power is Relative
"A toaster is lower power than a blast furnace"
Low Power specs can be more important than price
A cheap product that quickly drains the battery is too cheap
People complain on online product reviews
16-bit lower power than 32-bit
32-bit toggles twice the data paths than 16-bit
TI's MSP430 is one of the most popular (16-bit) cores BECAUSE it is “Ultra Low Power”
Microchip strong in 16-bit with their “eXtreme Low Power” PIC24F

9. Low Power Consumption Important for many 16-bit applications
Battery powered - increases battery life
Non-battery powered - increases system reliability
Other advantages
Uses inexpensive voltage regulator
Minimizes required board space
Eliminates heat sink or cooling fan

10. 16-bit Pin Compatibility with 8-bit
Upgrade your 8-bit in the same socket
Not all manufacturers have a pin-compatible 32-bit from their 8-bit
Specifications change
Your boss changes his mind
The board is laid out and your system is more complex than you thought
You can’t change your board and you need more:
Memory
Performance
Features
Magic smoke (just kidding)
A pin-compatible 16-bit device saves your career
“Pin Compatible” means:
Same electrical characteristics
Same peripherals, I/O, power pinout
Same Vcc and GND pins

11. Look at the Peripherals
Provides specific hardware functionality that is too impractical to perform in software
Two general types of peripherals
Digital peripherals
16-bit Timers
Serial I/O with 16-bit data registers
I/O ports
Analog peripherals
12-bit or 16-bit Analog-to-Digital (A/D) Converters
16-bit Digital-to-Analog (D/A) Converters
A 16-bit microcontroller reads 12-bit and 16-bit ADC registers in one easy cycle

12. Common Microcontroller Peripherals
System Requirement
Peripheral
Benefit
I/O Control
I/O Pins with bit level control
Direct interface to switches, actuators, and digital status signals
Serial Peripheral Communications
Serial ports: SPI, I2C, UART, CAN
Hardware support for expansion and external device communications
Precision control of actuators and motors
Sophisticated timers and PWM modules
Low software overhead control of signal
Quickly resolve complex software overhead control flow
Conditional jumps
Bit test instructions
Efficient program flow – quick, small code
Fast response to external events
External interrupts
Multiple interrupt levels
Interrupt priority control
Program control immediately redirected on event occurrence; minimal overhead
Measurement of sensor data
Analog-to-Digital Converters
Hardware support for external sensors

13. Microcontroller Peripherals – What’s Important
System Requirement
Peripheral
What’s Important
I/O Control
I/O Pins with bit level control
Electro-Static Discharge (ESD) rating, Current sink/source
Serial Peripheral Communications
Serial ports: SPI, I2C, UART, CAN, Ethernet, USB
Are there RAM Buffers?
Can it handle your flow of data?
Enough DMA channels?
Precision control of actuators and motors
Sophisticated timers and PWM modules
Interrupt configuration Intelligent timers
Quickly resolve complex software overhead control flow
Conditional jumps
Bit test instructions
Native bit manipulation? Additional instructions to set up?
Fast response to external events
External interrupts
Multiple interrupt levels
Interrupt priority control
Interrupt overhead? Shadow registers? Programmable priority?
Measurement of sensor data
Analog-to-Digital Converters
How fast is the A/D conversion? What is the accuracy ±LSB?

14. Pulse Width Modulation (PWM)
Used to generate regular external waveforms
Not the same as capture/compare timers
16-bit timers with a 16-bit core have lower software overhead than an 8-bit
Look for 16-bit microcontrollers that have PWM modules that require no software overhead to generate signals
Timer 1
Timer 2
Timer 3

15. 16-bit Microcontroller Using ADC, I/O, Timers in a System
Ex: Motor control system
A/D feeds back current draw information
16-bit ADC reads in one cycle
I/O pins feed back position detection information from encoder
16-bit Timers drive phase windings of motor
A/D
feedback
CapCom Timer
position detect
Microcontroller
phase a
Timers
phase e

16. What are Interrupts? Stops the execution of present software
Redirects the program flow based on an event
Two interrupt sources
External
Internal
Main loop executes code
Interrupt occurs
State of system is saved on stack
Program execution is redirected to an interrupt routine
Interrupt routine finishes
State of system is restored from stack
Code execution resumes at where it left off

17. External Interrupts
Tells the program to stop what it’s doing and recognize the interrupt
Typically an interrupt is generated on either a rising edge OR falling edge
But, some micros can generate an interrupt on any state change
Rising OR falling edge
Interrupts

18. Choosing a 16-bit Microcontroller Importance of Interrupts
There is overhead, in clock cycles, in saving the state of the system on the stack
There is overhead, in clock cycles, in restoring the state of the system on the stack
This overhead is hard-wired into the microcontroller. It is non-negotiable
For some 16-bit microcontrollers this overhead can be as low as 6 cycles or as long as 20 cycles.
All system functions of the microcontroller are locked and unavailable during this time
Sure, you can always increase the clock speed
Now you’re drawing more power
If interrupt latency and power draw isn’t important, you might as well look at a 32-bit

19. Common Features in a 16-bit Microcontroller
More communications stacks so a larger RAM-to-Flash ratio than 8-bit
Need performance around 16 to 70MIPS
Faster peripherals than an 8-bit
Common applications:
Motor control
User interface
Graphic display
Human interface
Digital power control
Switching power supplies
RTOS rarely used in 16-bit

20. Next: System Considerations
The End Part 4
Next: System Considerations