Renesas M32R/ECU Series, User Manual

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10
10-190
MULTIJUNCTION TIMERS
10.8 TOU (Output-Related 24-Bit Timer)
32180 Group User’s Manual (Rev.1.0)
10.8.16 Operation in TOU Continuous Output Mode (without Correction Function)
(1) Outline of TOU continuous output mode
In continuous output mode, the timer counts down starting from the set value of the counter and when the
counter underflows, it is loaded with the reload register value. Thereafter, this operation is repeated each
time the counter underflows, thus generating consecutive pulses whose waveform is inverted in width of
(reload register set value + 1).
When the timer is enabled after setting the counter and reload register, it starts counting down from the
counter’s set value synchronously with the count clock and when the minimum count is reached, generates
an underflow. This underflow causes the counter to be loaded with the content of the reload register and start
counting over again. Thereafter, this operation is repeated each time an underflow occurs. To stop the
counter, disable count by writing to the enable bit in software.
The F/F output waveform in continuous output mode is inverted (F/F output level changes from low to high or
vice versa) at startup and upon underflow, generating a waveform of consecutive pulses until the timer stops
counting. An interrupt request can be generated each time the counter underflows.
The (counter set value + 1) and (reload register set value + 1) are effective as count values. (For counting
operation, see also Section 10.3.11, “Operation of TOP Continuous Output Mode.”)
(2) Precautions on using TOU continuous output mode
The following describes precautions to be observed when using TOU continuous output mode.
• If the timer is enabled by external input in the same clock period as count is disabled by writing to the
enable bit, the latter has priority so that count is disabled.
• To read the counter on-the-fly, make sure the read timing does not coincide with an underflow of the 16
low-order bits (8 high-order bits decremented). When reading the counter on-the-fly, take the appropriate
measure to ensure that the read value is correct by, for example, reading the counter twice in succession.
• If the counter is accessed for read immediately after being reloaded pursuant to an underflow, the counter
value temporarily reads as H’FF FFFF but immediately changes to (reload value – 1) at the next clock
edge.
• Because the timer operates synchronously with the count clock, a count clock-dependent delay is in-
cluded before F/F output is inverted after the timer is enabled.