1. Embedded Microcontroller Systems
More interfacing and examples

2. Overview Performance metrics Synchronization methods
I/O Devices and hardware interface issues
Microcontroller in control systems
Control block diagrams
Actuators, plant, sensors
Open loop, closed loop control
Proportional and integral controllers

3. Performance Metrics
I/O Device uC
Latency – time delay between when I/O device is ready for service and when uC responds.
input device – time between when data is ready and when it is actually latched into uC
output device – time between when device is ready for new data and when it is sent.

4. Performance Metrics Latency Hardware delays in uC subsystems
I/O Device uC
Latency
Hardware delays in uC subsystems
Software delays

5. Performance Metrics
I/O Device uC
Throughput – maximum data flow (bytes per second) that can be processed from the I/O device.
can be limited by uC or by I/O device
can be reported as long term average or short term maximum

6. Performance Metrics
I/O Device uC
I/O Device
Priority – determines the order of service when more than two or more devices request at the same time.
determines if a high-priority device can suspend a low-priority request that is currently being processed.
may want to implement equal priority so that no device monopolizes the uC.

7. Real time systems Hard real-time – guarantees a maximum latency.
Soft real-time – system supports priority.

8. Synchronization Methods
I/O devices can be in one of 3 “states”
idle – disabled or inactive, no I/O occurs
busy – working on generating an input (input I/O) or accepting an output (output I/O)
done – ready for a new transaction.
Busy to done transitions cause status flags to become true.

9. Synchronization – Gadfly Loop
Polling loop
Gadfly loop
Busy-waiting loop – software checks status flag in a loop that does not exit until the status flag is set.
new data, gadfly loop completes
INPUT
DEVICE:
new input is
ready - done
waiting for
input - busy
software reads data, asks for another

10. Synchronization – Gadfly Scenarios No Buffering
Input Device:
busy
done
busy
done
uC software:
I/O bound
waiting for new
input
read
data
process
data
read
data
waiting
busy
done
Input Device:
read
data
waiting
uC software:
process
CPU bound

11. Synchronization – Gadfly Scenarios Buffering
Input Device:
As long as buffer is large enough, both software and I/O can operate at their maximum rate
busy
done
busy
done
busy
done
busy
BUFFER
process
data
read
data
process
data
read
data
process
data
uC software:

12. Synchronization – Blind Cycle
Software waits a fixed amount of time and assumes I/O will complete within the delay.
No status flag from I/O device.
Used for I/O that has predictable delays.
Input Device:
busy
done
busy
done
uC software:
process
data
read
data
process
data
read
data
waiting
waiting
fixed delay

13. Synchronization - Interrupts
Interrupts – hardware causes software to execute ISR.
Global data structures used to communicate data between main program and ISR.
Timer interrupts used to execute specific functions at regular intervals.

14. Synchronization - Interrupts
Use interrupts when:
Arrival times of input is variable.
There are other things to do in main program.
I/O is important (alarm, hardware failure) but infrequent.
Buffering can also be used with interrupts to allow for better throughput.
Must not forget that interrupts slow the main program loop!

15. Buffering – FIFO Queue
Producer (uC or I/O)
Consumer (uC or I/O)
Put
Get
FIFO
Data is received (Get) in the same order that it was transmitted (Put)
As long as FIFO is not full or empty, both producer and consumer operate at their own rate.
Need a way for producer and consumer to know if FIFO is full or empty.

16. Synchronization – Periodic Polling
Periodic polling – uses a clock/timer interrupt to periodically check the I/O status.
Used in cases where interrupts are desirable (there is much to do in the main program) but the I/O device does not support interrupts.
Keypad is an example – will investigate in the next exercise.

17. EE/CS-152: Microprocessors and Microcontrollers
Synchronization - DMA
Direct Memory Access – I/O transfers data directly to/from memory.
Requires a DMA controller between memory and I/O device.
Used when bandwidth and latency are important parameters.
Data transfer only – no processing of data.
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

18. EE/CS-152: Microprocessors and Microcontrollers
DMA
Burst mode DMA – a block transferred while the uC is halted
used when uC and DMA rates are similar
Cycle-stealing DMA – data is transferred during cycles when the uC is not using the bus.
used when uC rate is faster than I/O
DMA Controller
I/O
device uC
addr
Memory
data
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

19. Keypad – how slow can we go?
Slow I/O Interface
Keypad – how slow can we go?
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

20. I/O Devices and hardware interface issues
Overview:
Categories of I/O
Input and Output examples
Output actuator examples
DC Motor (analog and digital control)
Stepper Motor
Output display example
LCD display (parallel and serial)
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

21. EE/CS-152: Microprocessors and Microcontrollers
I/O Categories
Input devices
Sensors, User-input
Output devices
Actuators, Displays
Complex I/O devices (printers, faxes, coprocessors, etc)
Analog I/O Digital I/O
Voltage levels - Voltage levels
Current draw - Synchronization
Sampling frequency - Throughput
Noise Noise
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

22. EE/CS-152: Microprocessors and Microcontrollers
Input Examples
Sensors
light
force
sound
position
orientation
proximity
tactile
temperature
pressure
humidity
speed
acceleration
displacement
User input
keyboards
joysticks
mouse
keypad
switches
touchpad
dial
slider
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

23. EE/CS-152: Microprocessors and Microcontrollers
Output Examples
Actuators
motors
solenoids
relays
heaters
lights
piezoelectric materials (buzzers, linear actuator)
speakers
Displays
LED displays
LCD displays
CRT displays
indicator lights
indicator gauges
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

24. EE/CS-152: Microprocessors and Microcontrollers
Example – DC Motor
Important in LOTS of applications
cameras, drives, elevators, trains, robots…
Many types, but all work similarly:
Apply voltage across + and – leads, electrical energy is converted to mechanical energy.
For some range of voltage, the torque of the motor shaft is proportional to value of voltage.
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

25. DC Motor Current required by motor depends on how it is loaded.
Current is almost always more than the uC can provide.
Need an interface circuit between uC and motor.
Motor current (A)
stalled
loaded
no load
Applied voltage (volts)
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

26. Interfacing Motors Digital Outputs
Basic idea is to use a switch of some kind to isolate current in uC from motor current.
Motor is an inductor though, so it stores current.
Flyback diode used to route current away from switch when switch opens to avoid damage to switch.
flyback diode
External Voltage +
switch open current
switch closed
current
motor
Control signal from uC
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

27. Interfacing Motors Digital Outputs
H-Bridge – circuit topology that allows bi-directional control of motor.
Each switch controlled by an output of the uC.
Switches implemented by relays, solid-state switches, or transistors
Diodes omitted for simplicity. +
external
voltage -
motor
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

28. Interfacing Motors Analog Output
8051 DAC can provide up to 15 mA of current, up to 3.3V voltage.
Must provide both voltage and current amplification to drive a DC motor.
Amplifiers
Power MOSFETs
Motor driver ICs
Relays
used in the upcoming control lab
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

29. EE/CS-152: Microprocessors and Microcontrollers
Stepper Motors
Inherent digital interface
Can easily control both position and velocity
Used in disk drives, printers, etc.
Small, fixed rotation per change in control signals
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

30. EE/CS-152: Microprocessors and Microcontrollers
Basic Operation
Simplified stepper motor
5 “teeth”
360  5 = 72
moves 72 per “step”
Changing polarity of stator magnets causes step.
Typical stepper motors have 200 steps per revolution, with 1.8 per step. -
phase 2 + S5 N5 N1 +
phase 1 - S4 S1 N4 N2 S3 S2 N3
rotor
electromagnets
stator
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

31. Stepper Motor Interface
+Vmotor
VDD
4-phase
stepper
motor
Inverting
buffers
8051 A A’ B B’
port
pins
1010
1001
0101
0110
1.8
1.8 
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

32. Output Display Example: LCD Display
LCD – Liquid Crystal Display
Lower power than LED display
More flexible in size and shape
Slower response time
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

33. LCD Operation AC voltage required – DC voltage damages LCD
Control changes reflectivity of the liquid crystal material.
Actual light energy supplied by room light or back light.
front plane
CMOS
back plane
control
60 Hz
Oscillator
liquid crystal material
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

34. EE/CS-152: Microprocessors and Microcontrollers
LCD Interfacing
Simple parallel interface – similar to LED:
VDD
7-segment
LCD
Driver/Decoder
Separate Front Planes
8051 a b c d e f g A B C D
port
pins
Common Back Plane
60 Hz
Oscillator
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

35. EE/CS-152: Microprocessors and Microcontrollers
LCD Interfacing
Serial driver interface
MC LCD Driver
data in
data out
48 bit shift register
clock
48 bit latch register
BP1 BP2 BP3 BP4 FP1 FP2 FP3 FP4 FP5 FP6 FP7 FP8 FP9 FP10 FP11 FP12
48 segment LCD display
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

36. Using Microcontrollers for Control
Overview
Open-loop control systems
Simple closed-loop control systems
Closed-loop position control
PID controllers
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

37. EE/CS-152: Microprocessors and Microcontrollers
Some Terminology
Control variables – properties we want to control (position, velocity, temperature, etc)
Control commands – output to actuators
Driving forces – the actuator forces that cause the control variables to change (heat, force, etc)
Physical plant – the thing being controlled
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

38. Open-loop Control Systems
No feedback path from the plant
Note that these are all a function of time
Real control variables X(t)
Control commands U(t)
Driving Forces V(t)
Desired control variables X*(t)
Physical
Plant
Actuators uC
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

39. Open-loop Control Example
Stepper motor
Real control variables X(t)
Control commands U(t)
Driving Forces V(t)
Desired control variables X*(t)
Physical
Plant
Actuators uC
Inverting
driving
buffers
desired shaft position
specified in program uC
stepper
motor
shaft position
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

40. Open-loop Control Example
Traffic light controller
Inverting
driving
buffers uC
desired light pattern
in software
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

41. Closed-loop Control Feedback from plant to controller Physical
Real control variables X(t)
Control commands U(t)
Driving Forces V(t)
Desired control variables X*(t)
Physical
Plant
Actuators uC
Sensor
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

42. Closed-loop Control “Bang-bang control”
Bang-bang – control output can only turn something ON or OFF. No variable control.
Requires a “deadband” or “hysteresis” which defines a range of acceptable values for output - otherwise the control system components can wear out from too many switching cycles. (Relays, for example, have a limited lifetime).
Works well with physical plant with a slow response time.
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

43. Closed-loop Control Systems
Bang-bang control – temperature control example.
Desired temperature, Tlow < T < Thigh
“plant”
Flowchart of control algorithm
Heater
estimate T’ uC
T’ > Thigh
T’ < Tlow T’ T’
Temperature
sensor
Turn off
Leave
Turn on
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

44. Closed-loop Position Control
Incremental control – adds or subtracts a small constant from the output control command, U(t), in response to X(t) sensed.
Real control variables X(t)
Control commands U(t)
Driving Forces V(t)
Desired control variables X*t
Physical
Plant
Actuators uC +1 or -1
Sensor
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

45. EE/CS-152: Microprocessors and Microcontrollers
Incremental Control
Rate of sampling is very important
If sampling rate is too fast, actuators are saturated and a bang-bang system results.
If sampling rate is too slow, then controller will not keep up with plant.
Rule of thumb for rate: control execution rate is 10x the step response of the plant.
Must check for underflow and overflow after increment or decrement.
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

46. Closed-loop Control PID Controller
Faster and more accurate than previous systems.
Based on linear control theory.
Three components – sometimes fewer are used.
Proportional – output is linearly related to error signal.
Integral – output is related to integral of the error signal.
Derivative – output is related to derivative of the error.
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

47. PID Controller
To understand, must transform parts of control diagram into discrete time domain.
Very important to have periodic sampling and processing.
In the figure below, n is the sample number
Real control variables x(t)
Desired output x* +
e(n) uC
PID
controller
Physical
Plant
u(n)
p(t)
Actuator -
x’(n)
Sensor
error signal: e(n) = x*(n) - x’(n)
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

48. PID Controller u(t) = P(t) + I(t) + D(t) + uC Physical Plant - Sensor
Proportional – output is proportional to error input
Continuous time: P(t) = Kp * E(t)
Discrete time: P(n) = Kp * E(n)
Actual
Output x(t)
Desired output x* +
e(n) uC
PID
controller
Physical
Plant
u(n)
p(t)
Actuator -
x’(n)
Sensor
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

49. PID Controller u(t) = P(t) + I(t) + D(t) Ki large Ki small
Integral – output is proportional to integral of error signal
Continuous time: I(t) = Ki E(t) dt
Discrete time: I(n) = Ki  E(n) t = Ki t  E(n)
I(n)
e(t)
Ki large n t
Ki small
I(t)
I(n)
I(n) t t n n
t is sampling period
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

50. Equation for Integral Component
Discrete time: I(n) = Ki t  E(n)
integral += errorsig; //integral = integral + errorsig
//integral is sum of errorsignals
//integral includes: M_MEAS samples of error
//multiplied by GAIN_PRECISION
...
output = Kp*errorsig / M_MEAS/GAIN_PRECISION +
Ki * integral / M_MEAS / SAMPLERATE /GAIN_PRECISION
= 1/t
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

51. PID Controller u(t) = P(t) + I(t) + D(t)
Derivative – output is proportional to derivative of error signal
Continuous: D(t) = Kd* dE dt
E(n) – E(n-1) t
Discrete: D(n) = Kd *
t is sampling period
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

52. PI Controller for Position Control
(we will not use the derivative term, which can cause instability)
Desired position
1*
(potentiometer)
Actual
position 2(t) uC PI
controller DC
Motor
uf(n)
Servo
Amplifier
p(t)
2(n)
ub(n)
potentiometer
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

53. PI Controller Hardware Setup
8051
Microcontroller
setpoint
potentiometer
ADC0.0
Input
voltage
conversion
interface
-15 to +15V V
multiplexor
ADC0
ADC0.1
to SA1SOD
Input 1
output
potentiometer
DAC0
Output
voltage
conversion
interface
-15 to +15V V
DAC0 V
to SA1SOD
Input 2
DAC1
DAC1 V
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

54. EE/CS-152: Microprocessors and Microcontrollers
Circuit Schematics for Interface Circuits
Input voltage conversion interface
Output voltage conversion interface
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

55. EE/CS-152: Microprocessors and Microcontrollers
PI Control Algorithm
Controller must execute the following tasks:
Sample inputs
Compute error value
Compute integral value
Compute output signal from error value, integral value and preset Kp and Ki.
Send computed output signals to amplifier
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

56. Controller Performance Metrics
Stability – a requirement
Response time – how fast the output responds to the input.
Steady state error – how much the output differs from the input after it has settled.
For position controller – DEADBAND is a measure of the steady state error.
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

57. Total DeadBand Measurements
input position
output position 1 2
DB (1) = 1- 2
repeat for a negative angle, - 1
DB (-1) = 2- 1
TDB(1) = |DB(1)| + | DB(-1)|
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers

58. EE/CS-152: Microprocessors and Microcontrollers
Control your position!
Prelab – software only
Prof. Cherrice Traver
EE/CS-152: Microprocessors and Microcontrollers