R8C/20 Group, R8C/21 Group 14. Timers
Rev.2.00 Aug 27, 2008 Page 135 of 458
REJ09B0250-0200
Figure 14.12 Operating Example of Pulse Period Measurement Mode
Underflow signal of timer
RA prescaler
NOTES:
1. The contents of the read-out buffer can be read when the TRA register is read in pulse period measurement mode.
2. After an active edge of measurement pulse is input, the TEDGF bit in the TRACR register is set to 1 (active edge found) when the timer RA
prescaler underflows for the second time.
3. The TRA register should be read before the next active edge is input after the TEDGF bit is set to 1 (active edge found).
The content in the read-out buffer is retained until the TRA register is read. If the TRA register is not read before the next active edge is
input, the measured result of the previous period is retained.
4. When set to 0 by a program, use a MOV instruction to write 0 to the TEDGF bit in the TRACR register. At the same time, write 1 to the
TUNDF bit in the TRACR register.
5. When set to 0 by a program, use a MOV instruction to write 0 to the TUNDF bit. At the same time, write 1 to the TEDGF bit.
6. The TUNDF and TEDGF bits are both set to 1 if the timer RA underflows and reloads on an active edge simultaneously.
0Eh 0Dh 0Fh 0Eh 0Dh 0Ch 0Bh 0Ah 09h 0Fh 0Eh 0Dh 01h 00h 0Fh 0Eh0Fh
0Dh
0Fh 0Bh 0Ah 0Dh 01h 00h 0Fh 0Eh09h
TSTART bit in
TRACR register
1
0
1
0
1
0
TEDGF bit in
TRACR register
1
0
Measurement pulse
(TRAIO pin input)
Contents of TRA
1
0
Contents of read-out
buffer
(1)
IR bit in TRAIC
register
TUNDF bit in
TRACR register
Set to 1 by program
Starts counting
TRA reloads
TRA read
(3)
Retained
(4)
(2)
(2)
Set to 0 by program
(5)
(6)
Conditions: A period from one rising edge to the next rising edge of measurement pulse is measured (TEDGSEL = 0) with
the default value of the TRA register as 0Fh.
0Eh
TRA reloads
Retained
Set to 0 when interrupt request is acknowledged, or set by program
Set to 0 by program
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