Datasheet

V850ES/JG3 CHAPTRER 8 16-BIT TIMER/EVENT COUNTER Q (TMQ)
R01UH0015EJ0300 Rev.3.00 Page 365 of 870
Sep 30, 2010
(d) Processing of overflow if capture trigger interval is long
If the pulse width is greater than one cycle of the 16-bit counter, care must be exercised because an overflow
may occur more than once from the first capture trigger to the next. First, an example of incorrect processing is
shown below.
Example of incorrect processing when capture trigger interval is long
FFFFH
16-bit counter
0000H
TQ0CE bit
TIQ0m pin input
TQ0CCRm register
INTTQ0OV signal
TQ0OVF bit
D m0 D m1
D m0
D m1
<1> <2> <3> <4>
1 cycle of 16-bit counter
Pulse width
The following problem may occur when a long pulse width in the free-running timer mode.
<1> Read the TQ0CCRm register (setting of the default value of the TIQ0m pin input).
<2> An overflow occurs. Nothing is done by software.
<3> An overflow occurs a second time. Nothing is done by software.
<4> Read the TQ0CCRm register.
Read the overflow flag. If the overflow flag is 1, clear it to 0.
Because the overflow flag is 1, the pulse width can be calculated by (10000H + D
m1 − Dm0)
(incorrect).
Actually, the pulse width must be (20000H + D
m1 − Dm0) because an overflow occurs twice.
If an overflow occurs twice or more when the capture trigger interval is long, the correct pulse width may not be
obtained.
If the capture trigger interval is long, slow the count clock to lengthen one cycle of the 16-bit counter, or use
software. An example of how to use software is shown next.