Microcontroller: Timers, ADC

Transcription

1 Microcontroller: Timers, ADC Amarjeet Singh February 1, 2013

2 Logistics Please share the JTAG and USB cables for your assignment Lecture tomorrow by Nipun 2

3 Revision from last class When servicing an interrupt, how does the timing work? How are interrupt priorities decided? What are the primary blocks in a Timer/Counter? How is Buffer Value (BV) flag decided in both Capture and Compare mode in xmega? 3

4 xmega: Timer/Counter Block Diagram Registers: Counter (CNT), Period (PER), Compare Capture (CCx) Size? Counter compared with 0 or PER to generate BOTTOM/TOP Compared with CCx to generate interrupt, events Waveform generator mode uses CCx to set waveform period and pulse width How to support 32 bit count? 4

5 Single Slope PWM Generation Time period is controlled by PER register (counter counts from BOTTOM to TOP) while CCx register controls the duty cycle New value of CCx Register loaded on UPDATE event WG output is set to 0 on compare match and set to 1 on TOP 5

6 Dual Slope PWM Generation Time period is controlled by PER register (counter counts from BOTTOM to TOP and then TOP to BOTTOM) while CCx register controls the duty cycle WG output is set to 1 on BOTTOM ; 0 on compare match during up count and 1 on compare match during down count New value of CCx updated on UPDATE event 6

7 Timer/Counter 0/1: Associated Registers 7

8 Timer/Counter 0/1: Associated Registers 8

9 xmega: Timer/Counter2 Realized when Timer/Counter 0 is set in split mode A system of 2 8-bit Timer Counters (referred to as Low Byte and High Byte Timer/Counter) with 4 compare channels each Provides 8 configurable PWM channels with individually controlled duty cycle Only the low byte timer/counter can be used to generate compare match interrupts, events Shared clock source and separate period and compare settings At a time can be only used as Timer/Counter 0 or 2 9

10 Timer/Counter2: Block Diagram Counter operation same as Timer/Counter 0 Compare channel operation same as Timer/Counter 0 10

11 xmega Timers: Summary TC-0/1: 16-bits, 32-bits support by cascading TC-2: 2 8-bits Multiple compare or capture (CC) channels for each timer One compare match or input capture interrupt/event per channel Used for count and direction control, capture Waveform generation: Frequency generation Single slope PWM (Only this one available for TC-2) Dual slope PWM Input capture: Frequency capture Pulse-width capture 11

12 Pic24F: Timers and Counters Timer1: 16-bit timer/counter Timer2/3 and Timer4/5: 32-bit timers that can be independently configured as 2 16-bit counters Separate module for Input Capture (on ICx pin) Can capture rising/falling/both edges 12

13 Pic24F: Timers and Counters Separate output compare module to generate output pulses 13

14 AVR32: Timers and Counters 14

15 xmega: Real Time Counter (RTC) 16-bit RTC runs continuously even in the low power sleep mode to keep track of time Can wake up devices from sleep and/or generate interrupt at regular time intervals Reference clock is typically 1.024KHz output from high accuracy crystal of KHz Includes a 10-bit prescaler to scale down the reference clock before it reaches the counter What is the highest resolution with KHz clock? With a resolution of 1 s what is the maximum timeout period? 15

16 xmega: Real Time Counter (RTC) RTC can generate both interrupts and events Compare interrupt Overflow interrupt 16

17 xmega: RTC32 32-bit Real Time Counter Runs continuously even in low power sleep mode External KHz clock must be used as clock reference fed into the prescaler Reference clock: 1 Hz or KHz 17

18 PIC24F: Real Time Clock and Calendar Time (hours, minutes, seconds); Calendar (Weekday, date, month, year): Year range (with leap year correction) Requires external KHz clock crystal Optimized for low power operation 18

19 xmega: Analog Comparators Compares voltage levels on two inputs and gives a digital output based on the comparison Input sources: Analog port pins, several internal signals, 64- level programmable voltage scales the input values on positive pin AIN0 and negative pin AIN1 19

20 Analog Comparator When voltage on first input is greater than that on second input, Analog Comparator Output (ACOUT) is set Output can be set to trigger Timer/Counter Capture operation or can also trigger interrupt specific to analog comparator Interrupt triggering can be enabled on output rise, fall or toggle How can I use both AC0 and AC1 to check if input signal is within a range? Window mode supported internally by the device 20

21 Analog to Digital Converter (ADC) 12-bit resolution (Can also work in faster 8-bit resolution) Up to 2 million samples per second (minimum 3.5 us conversion time) Flexible input selection: Both single ended and differential Up to 16 single-ended input; 4 channels of differential (with/without gain) Built in differential gain: 1/2x 64x Multiple input sources Internal temperature sensor, DAC output etc. 21

22 Analog to Digital Converter (ADC) Pipelined architecture with several stages: Allows high sample rate at low system clock frequency New input can be sampled while older ADC conversions still going on 4 conversion channels with individual input selection: Allow 4 parallel operations 22

23 ADC Voltage Conversion Several sources for reference voltage selection Result is written to corresponding Channel result register (RES) Global setting for signed/unsigned conversion Unsigned for single ended or internal signals Signed for differential signals generating both positive and negative results What will be the TOP value for signed/unsigned conversion? What will be the ADC transfer function in terms of TOP? 23

24 ADC Voltage Conversion: Signed mode Single ended measurement in signed mode: Negative connected to ground ADC transfer function in signed mode 24

25 ADC Voltage Conversion: Signed mode Signed differential input ADC transfer function in signed mode 25

26 ADC Voltage Conversion: Unsigned mode Single ended measurement in unsigned mode: Negative connected to half the reference voltage minus a fixed offset (nominal value 0.05*V REF ) Positive will vary from 0 to V REF Offset to allow calibration when internal ground is higher than external ground ADC transfer function in unsigned mode 26

27 xmega: ADC Compare function: ADC has in-built 12-bit compare function ADC value can be compared with the ADC Compare Register to generate an interrupt/event if the value is above/below the threshold All 4 ADC channels share the same Compare Register Starting a conversion: Select the input source for one or more ADC channels ADC conversion started by application software writing to start conversion bit of the Channel or from any events in the Event System 27

28 xmega ADC Block Diagram 28

29 ADC Clock and Conversion Timing Clocked from Peripheral Clock that can be prescaled to provide ADC Clock Maximum ADC sampling rate given by ADC clock frequency Propagation delay of ADC measurement given by RES: Resolution (8- or 12-bit) Greater than one clock cycle but pipelined architecture implies sampling rate is not limited by propagation delay but by clock frequency 29

30 ADC Clock and Conversion Timing MSB of the result is converted first Rest of the bits are converted in the next 3 (for 8-bit resolution) or 5 (12-bit resolution) clock cycles Converting 1 bit takes half a clock cycle During the last clock cycle, result is prepared before the interrupt flag is set Single conversion without Gain 30

31 ADC Clock and Conversion Timing Single Conversion with Gain 31

32 ADC Clock and Conversion Timing Single Conversion on 2 ADC Channels (both without Gain) Both conversion requests may be placed at the same time Due to pipelined design, second conversion can start in the next clock cycle after the first conversion has started 32

33 ADC Clock and Conversion Timing Single Conversion on 2 ADC Channels (Channel0 with Gain and Channel1 without Gain) 33

34 ADC Clock and Conversion Timing Single Conversion on 2 ADC Channels (Channel0 without Gain and Channel1 with Gain) 34

35 ADC Clock and Conversion Timing Free Running mode (All 4 channels Channel 0 and 1 without gain, Channel 2 and 3 with Gain) 35

36 What did you learn today? On a small sheet of paper, give me a short (2-3 sentences) description of what you learned today You can use it to give any broad comments on the class as well 36