Renesas M16C FAMILY, User Manual

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Rev.2.00 Oct 16, 2006 page 18 of 354
REJ09B0340-0200
M30245 Group 2. Timer A
Figure 2.2.12. Operation timing of event counter mode, reload type selected
2.2.5 Operation of Timer A (event counter mode, reload type selected)
In event counter mode, choose functions from those listed in Table 2.2.4. Operations of the circled items
are described below. Figure 2.2.12 shows the operation timing, and Figure 2.2.13 shows the set-up
procedure.
Note: j = i – 1, but j = 4 when i = 0.
(1) Setting the count start flag to “1” causes the counter to count the falling edges of the count
source.
(2) If an underflow occurs, the content of the reload register is reloaded, and the count continues.
At this time, the timer Ai interrupt request bit goes to “1”.
(3) If switching from an up count to a down count or vice versa while a count is in progress, the
switch takes effect from the next effective edge of the count source.
(4) Setting the count start flag to “0” causes the counter to hold its value and to stop.
(5) If an overflow occurs, the content of the reload register is reloaded, and the count continues.
At this time, the timer Ai interrupt request bit goes to “1”.
Operation
Table 2.2.4. Choosed functions
Item Item Set-up Set-up
Count source
Input signal to TAi
IN
(counting falling edges)
Input signal to TAi
IN
(counting rising edges)
TAj overflow
Count operation type Reload type
Free-run type
Factor for switching
between up and
down Content of up/down flag
Input signal to TAi
OUT
Pulse output function No pulses output
Pulses output
O
O
O
O
FFFF
16
n
0000
16
Time
Counter content (hex)
n = reload register content
(1) Start count
Count start flag
“1”
Set to “1” by software
“0”
Timer Ai interrupt
request bit
“1”
“0”
Up/down flag
“1”
“0”
Set to “1” by software
Set to “1” by software
(5) Overflow
Cleared to “0” when interrupt request is accepted, or cleared by software
Start count again
AAAA
(2) Underflow
AAAA
AAAA
(3) Switch count
Cleared to “0” by
software
(4) Stop count