CHAPTER 7 TIMER/COUNTER FUNCTION
User’s Manual U13850EJ4V0UM
194
(3) Pulse width measurement with free-running counter and two capture registers
When 16-bit timer register n (TMn) is used as a free-running counter (refer to
Figure 7-19
), the pulse width of the
signal input to the TIn0 pin can be measured.
When the edge specified by bits 4 and 5 (ESn00 and ESn01) of prescaler mode register n0 (PRMn0) is input to
the TIn0 pin, the value of TMn is loaded to 16-bit capture/compare register n1 (CRn1), and an external interrupt
request signal (INTTMn1) is set.
The value of TMn is also loaded to 16-bit capture/compare register n0 (CRn0) when an edge reverse to the one
that triggers capturing to CRn1 is input.
The edge of the TIn0 pin is specified by bits 4 and 5 (ESn00 and ESn01) of prescaler mode register n (PRMn0).
The rising or falling edge can be specified.
The valid edge of TIn0 is detected through sampling at a count clock cycle selected by prescaler mode register
n0, n1 (PRMn0, PRMn1), and the capture operation is not performed until the valid level is detected two times.
Therefore, noise with a short pulse width can be removed.
Caution If the valid edge of the TIn0 pin is specified to be both the rising and falling edges,
capture/compare register n0 (CRn0) cannot perform its capture operation.
Figure 7-19. Control Register Settings for Pulse Width Measurement
with Free-Running Counter and Two Capture Registers
(a) 16-bit timer mode control registers 0, 1 (TMC0, TMC1)
TMCn3
TMCn2
TMCn1
OVFn
TMCn
0
0
0
0
0
1
0/1
0
Free-running mode
(b) Capture/compare control registers 0, 1 (CRC0, CRC1)
CRCn2
CRCn1
CRCn0
CRCn
0
0
0
0
0
1
1
1
CRn0 as capture
register
Captures to CRn0 at
edge reverse to valid
edge of TIn0 pin.
CRn1 as capture
register
Remark
0/1: When these bits are reset to 0 or set to 1, other functions can be used along with the pulse
width measurement function. For details, refer to
7.1.4 Timer 0, 1 control registers
.
Содержание MPD703030A
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