Điện, điện tử - Chapter 7: Timing generation and measurements

Chapter 7 Timing generation and measurements 7.1 Timer functions Microcomputer principles and applications • Stop watch. • Captures time of external events. • Creates output waveform. • Pulse accumulations. • Creates periodic interrupts. 7.1 Timer functions Microcomputer principles and applications Triangle Sine Ramp up Ramp down Square Pulse 7.2 MSP430 Timer Microcomputer principles and applications • Asynchronous 16-bit timer/counter with four operating modes. • Selectable and configurable clock source. • Two or three configurable capture/compare registers. • Configurable outputs with PWM capability. • Asynchronous input and output latching. • Interrupt vector register for fast decoding of all Timer A interrupts. 7.3 Timer A Microcomputer principles and applications Generally MSP430 family contains two categories of timers • Timer A • Timer B. What is the difference between Timer A and Timer B? Same in operation, but Timer B is more sophisticated than Timer A and it has many features available than compared with Timer A. They are: • Bit-length of the timer is programmable as 8-bit, 10- bit, 12-bit, 16-bit. • Some Timers in B category have 7 CCR registers whereas the Timer A contains three capture/compare registers. • It contains double-buffered CCR register. • CCR register can be grouped. 7.3 Timer A Microcomputer principles and applications How many timers are there in MSP430G2553? There are two 16-bit timers are available in MSP430G2553, excluding watch dog timer. • Timer A0. • Timer A1. Each 16-bit timer starts counts from 0 to 0x0FFFF (0 to 65536) and they operate in four different modes: • Stop mode - Timer is in halt state or stops the timer. • Up mode - Timer counts up from zero to value stored in TACCR0 register (other than 0xFFFF) and roll over to zero after it reached the count value. Generally this mode used to produce time delays. 7.3 Timer A Microcomputer principles and applications • Continuous mode - it is same as UP mode but here Timer counts up from zero to maximum value 0xFFFFh and rolls over to zero after it reached 0xFFFF and keep going. • Up/Down mode- in this mode time counts up from 0 to TACCR0 register and then counts down back to zero as shown in figure. It is good for generating PWM’s and driving motors. 7.3 Timer A Microcomputer principles and applications TACCR0 0FFFFh TACCR0 0FFFFh TACCR0 0FFFFh Up mode Continous mode Up/Down mode 7.3 Timer A Microcomputer principles and applications 00 01 10 11 Divider 1/2/4/8 16-bit timer TAR Clear RC CCR0 Count mode EQU0 Set TAIFG CCR1 CCR2 TACLR 015 TASSELx IDx Timer clock MCx TACLK ACLK SMCLK INCLK 7.3 Timer A Microcomputer principles and applications • CCR0, CCR1, CCR2 (Compare/Capture Registers) are used to load the timer count. • TAR (Timer A Register) is the 16-bit timer register in which the count start increment/decrements value depends upon the timer mode settings. • CCIFG interrupt flag is set when the timer counts to the value stored in CCR0 register. • TAIFG interrupt flag is set when the timer count from CCR0 to zero. • TASSELx are the bits used to select one of the clock signals. • IDx bit are used to divide the clock signal applied to timer. • MCx bits are used select count mode. • TACLR bit clears the TAR register, clock divider and count direction (mode). 7.4 Timer A Output modes Microcomputer principles and applications OUTMODE.x Mode Description 000 Output The output signal OUTx is defined by the OUTx bit. The OUTx signal updates im- mediately when OUTx is updated. 001 Set The output is set when the timer counts to the TACCRx value. It remains set until a reset of the timer, or until another output mode is selected and affects the output. 010 Toggle/Reset The output is toggled when the timer counts to the TACCRx value. It is reset when the timer counts to the TACCR0 value. 011 Set/Reset The output is set when the timer counts to the TACCRx value. It is reset when the timer counts to the TACCR0 value. 7.4 Timer A Output modes Microcomputer principles and applications OUTMODE.x Mode Description 100 Toggle The output is toggled when the timer counts to the TACCRx value. The output period is double the timer period. 101 Reset The output is reset when the timer counts to the TACCRx value. It remains reset un- til another output mode is selected and af- fects the output. 110 Toggle/Set The output is toggled when the timer counts to the TACCRx value. It is set when the timer counts to the TACCR0 value. 111 Reset/Set The output is reset when the timer counts to the TACCRx value. It is set when the timer counts to the TACCR0 value. 7.4 Timer A Output modes Microcomputer principles and applications Example: Timer in Up Mode TACCR0 0FFFFh TACCR1 Output mode 1: Set Output mode 2: Toggle/Reset Output mode 3: Set/Reset Output mode 4: Toggle Output mode 5: Reset Output mode 6: Toggle/Set Output mode 7: Reset/Set EQU0 EQU1 EQU1EQU0 EQU0 TAIFG TAIFG TAIFG Interrupt events 7.5 Timer A interrupts Microcomputer principles and applications There are two interrupt flags (CCIFG and TAIFG) and its corresponding two interrupt vectors (TACCR0 and TAIV) available for Timers in MSP430. 7.5 Timer A interrupts Microcomputer principles and applications Timer block TACCR0 TAIV TAIFG CCR0 CCIFG CCR1 CCIFG CCR2 CCIFG Interrupt vectors 7.6 Timer A registers Microcomputer principles and applications TACTL - Timer A Control Register 15 14 1213 11 10 89 7 6 45 3 2 01 rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) Timer_A clock source select (INCLK is device-specific and is often assigned to the inverted TBCLK) (see the device-specific data sheet) Unused Bits 15-10 Unused TASSELx Bits 9-8 00 TACLK 01 ACLK 10 SMCLK 11 INCLK Unused TASSELx UnusedMCx TACLR TAIE TAIFGMCxIDx 7.6 Timer A registers Microcomputer principles and applications TACTL - Timer A Control Register 15 14 1213 11 10 89 7 6 45 3 2 01 rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) Input divider. These bits select the divider for the input clockIDx Bits 7-6 00 01 10 11 /1 /2 /4 /8 Mode control . Setting MCx = 00h when Timer_A is not in use conserves power.MCx Bits 5-4 00 01 10 11 Stop mode: the timer is halted. Up mode: the timer counts up to TACCR0. Continuous mode: the timer counts up to 0FFFFh. Up/down mode: the timer counts up to TACCR0 then down to 0000h. Unused TASSELx UnusedMCx TACLR TAIE TAIFGMCxIDx 7.6 Timer A registers Microcomputer principles and applications TACTL - Timer A Control Register 15 14 1213 11 10 89 7 6 45 3 2 01 rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) Unused Bit 3 Unused TACLR Bit 2 Timer_A clear. Setting this bit resets TAR, the clock divider, and the count direction. The TACLR bit is automatically reset and is always read as zero. TAIE Bit 1 Timer_A interrupt enable. This bit enables the TAIFG interrupt request. 0 1 Interrupt disabled Interrupt enabled TAIFG Bit 0 Timer_A interrupt flag. 0 1 No interrupt pending Interrupt pending Unused TASSELx UnusedMCx TACLR TAIE TAIFGMCxIDx 7.6 Timer A registers Microcomputer principles and applications TAR - Timer A Register 15 14 1213 11 10 89 7 6 45 3 2 01 rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) TARx Bits 15-0 Timer_A register. The TAR register is the count of Timer _A. TARx TARx 7.6 Timer A registers Microcomputer principles and applications TACCRx - Timer A Capture/Compare Register 15 14 1213 11 10 89 7 6 45 3 2 01 rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) TACCRx Bits 15-0 Timer_A capture/compare register. Compare mode: TACCRx holds the data for the comparison to the timer value in the Timer_A Register, TAR. Capture mode: The Timer_A Register, TAR, is copied into the TACCRx register when a capture isperformed . TARx TARx 7.6 Timer A registers Microcomputer principles and applications TACCTLx - Timer A Capture/Compare Control Register 15 14 1213 11 10 89 7 6 45 3 2 01 CCISx rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) r r0 rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) r rw-(0) rw-(0) rw-(0) Capture modeCMx Bits 15-14 00 No capture 01 Capture on rising edge 10 11 CAPCMx Capture on fallig edge Capture on both rising and falling edges Capture/compare input select. These bits select the TACCRx input signal. See the device-specific data sheet for specific signal connections. CCISx Bits 13-12 00 CCIxA 01 10 11 CCIxA GND Vcc SCS Bit 11 Synchronize capture source. This bit is used to synchronize the capture input signal with the timer clock. 0 1 Asynchronous capture Synchronous capture UnusedSCCISCS CCIFGOUTMODx COVOUTCCICCIE 7.6 Timer A registers Microcomputer principles and applications TACCTLx - Timer A Capture/Compare Control Register 15 14 1213 11 10 89 7 6 45 3 2 01 CCISx rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) r r0 rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) r rw-(0) rw-(0) rw-(0) Synchronized capture/compare input. The selected CCI input signal is latched with the EQUx signal and can be read via this bit SCCI Bit 10 Unused Bit 9 Unused. Read only. Always read as 0. TACLR Bits 7 - 5 Output mode. Modes 2, 3, 6, and 7 are not useful for TACCR0, because EQUx = EQU0. CAPCMx SCS Bit 8 Capture mode 0 1 Compare mode Capture mode 000 001 010 011 OUT bit value Set Toggle/reset Set/reset 100 101 110 111 Toggle Reset Toggle/set Reset/set UnusedSCCISCS CCIFGOUTMODx COVOUTCCICCIE 7.6 Timer A registers Microcomputer principles and applications TACCTLx - Timer A Capture/Compare Control Register 15 14 1213 11 10 89 7 6 45 3 2 01 CCISx rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) r r0 rw-(0) rw-(0) rw-(0) rw-(0) rw-(0) r rw-(0) rw-(0) rw-(0) CAPCMx UnusedSCCISCS CCIFGOUTMODx COVOUTCCICCIE CCIE Bit 4 Capture/compare interrupt enable. This bit enables the interrupt request of the corresponding CCIFG flag. 0 1 Interrupt disabled Interrupt enabled CCI Bit 3 Capture/compare input. The selected input signal can be read by this bit. OUT Bit 2 Output. For output mode 0, this bit directly controls the state of the output . 0 1 Output low Output high COV Bit 1 Capture overflow. This bit indicates a capture overflow occurred. COV must be reset with software. 0 1 No capture overflow occurred Capture overflow occurred CCIFG Bit 0 Capture/compare interrupt flag 0 1 No interrupt pending Interrupt pending 7.6 Timer A registers Microcomputer principles and applications TAIV - Timer A Interrupt Vector Register 10 8 r0 r0 9 r0 11 r0 12 r0 13 r0 14 r0 15 r0 2 0 r-(0) r0 1 r-(0) 3 r-(0) 4 r0 5 r0 6 r0 7 r0 00000000 0000 TAIVx 0 TAIV contents Interrupt Source Interrupt flag Interrupt priority 00h No interrupt pending - Highest 02h Capture/Compare TACCR1 CCIFG - 04h Capture/Compare TACCR2 CCIFG - 06h Reserved - - 08h Reserved - - 0Ah Timer overflow TAIFG - 0Ch Reserved - - 0Eh Reserved - Lowest