R8C/1A Group, R8C/1B Group
14. Timers
Rev.1.30
Dec 08, 2006
Page 121 of 315
REJ09B0252-0130
Figure 14.10
Operating Example in Pulse Period Measurement Mode
Underflow signal of
prescaler X
NOTES :
1. The contents of the read-out buffer can be read by reading the TX register in pulse period measurement mode.
2. After an active edge of the measured pulse is input, the TXEDG bit in the TXMR register is set to 1 (active edge found)
when the prescale X underflows for the second time.
3. The TX register should be read before the next active edge is input after the TXEDG bit is set to 1 (active edge found).
The contents in the read-out buffer are retained until the TX register is read. If the TX register is not read before the next
active edge is input, the measured result of the previous period is retained.
4. To set to 0 by a program, use a MOV instruction to write 0 to the TXEDG in the TXMR register. At the same time,
write 1 to the TXUND bit.
5. To set to 0 by a program, use a MOV instruction to write 0 to the TXUND in the TXMR register. At the same time,
write 1 to the TXEDG bit.
6. Bits TXUND and TXEDG are both set to 1 if timer X underflows and reloads on an active edge simultaneously.
0Dh 0Fh 0Eh 0Dh 0Ch 0Bh 0Ah 09h 0Fh 0Eh 0Dh
01h 00h 0Fh 0Eh
0Fh
0Dh
0Fh
0Bh
0Dh
01h
0Fh 0Eh
09h
TXS bit in TXMR
register
TXEDG bit in
TXMR register
1
0
CNTR0i pin input
Contents of timer X
Contents of
read-out buffer1
IR bit in
TXIC register
IR bit in INT1IC
register
TXUND bit in
TXMR register
Set to 1 by program
Starts
counting
Timer X
reloads
Retained
Timer X read
(3)
Retained
Set to 0 by program
(4)
(2)
(2)
(6)
Timer X read
(3)
Timer X
reloads
Timer X
reloads
Set to 0 by program
(5)
Set to 0 when interrupt request is acknowledged, or set by program
Set to 0 when interrupt request is acknowledged, or set by program
1
0
1
0
1
0
1
0
1
0
00h
0Ah
0Eh
Conditions: The period from one rising edge to the next rising edge of the measured pulse is measured (R0EDG = 0)
with the default value of the TX register as 0Fh.
i = 0 to 1
0Eh
