Transcript ECE 447 Fall 2009

ECE 447 Fall 2009
Lecture 10: TI MSP430
Timers and Capture Modes
Timer_A Overview
• Timer Block
–
–
–
–
The core, based on 16-bit register TAR
Can chose sources for clock and freq division
Timer block has no output
Flag TAIFG is raised when counter returns to 0
• Capture/compare channels
–
–
–
–
Capture an input, record value in TAR triggered by TACCRn
Compare TAR with the value stored in TACCRn
Request an Interrupt by setting its flag TACCRn CCFIG
Sample an input at a compare event
ECE 447: MSP430 Timer_A System
1. Generating delays - imposing a specific delay
between two points in the program by polling.
label 1 instr1
instr2
label2
instrN
delay
ECE 447: MSP430 Timer_A System
2. Input capture - measuring the time between signal
edges
start
start
stop
stop
3. Output compare - generating signals with the given
timing characteristics
single pulse
pulse width
periodical signal
period
ECE 447: MSP430 Timer_A System
4. Real Time Clock– Produce a periodic signal for
the MSP430.
period
The Real Time Clock Interrupt implements a hardware
based time of day clock that can be used by the
software.
ECE447: MSP430 Timer I/O Pins and
Channels - 4618
ECE447: MSP430 Compare/Capture Block
Diagram.
MSP430xx4xx Implementation of Timer_A
Timer_A Interrupt Schematic
Timer_A MSP430xx4xx Registers
TACTL: Timer_A Control Register
TAR: Timer_A Register
TACCRx: Timer_A Capture/Compare Register
TACCTLx: Capture/Compare Control Register
TAIV: Timer_A Interrupt Vector Register
ECE447: MPS430 Timer_A input clocks and
dividers
ECE447: Measuring Pulse Widths
100 s < width < Configured Period (previous table)
stop
start
width  100 s
start stop
width  Configured Period (previous table)
start
Timer overflows
stop
ECE 447: Measuring intervals
<216 clock cycles
FFFF
stop
start
0
ECE 447: Measuring intervals <216
clock cycles (overflow)
1
2
FFFF
start
stop
0
ECE 447: Measuring intervals
>216 clock cycles
1
2
N=3
FFFF
stop
R
start
0
ECE 447: Measuring intervals
>216 clock cycles
1
FFFF
start
2
3
N=4
R1
R1+R2=R
0
stop
R2