
2.3.4.1
Warm-up counter operation when the oscillation is enabled by the hardware
(1)
When a power-on reset is released or a reset is released
The warm-up counter serves to secure the time after a power-on reset is released before the supply
voltage becomes stable and the time after a reset is released before the oscillation by the high-frequency
clock oscillation circuit becomes stable.
When the power is turned on and the supply voltage exceeds the power-on reset release voltage, the
warm-up counter reset signal is released. At this time, the CPU and the peripheral circuits are held in
the reset state.
A reset signal initializes WUCCR<WUCSEL> to "0" and WUCCR<WUCDIV> to "11", which se-
lects the high-frequency clock (fc) as the input clock to the warm-up counter.
When a reset is released for the warm-up counter, the high-frequency clock (fc) is input to the warm-
up counter, and the 14-stage counter starts counting the high-frequency clock (fc).
When the upper 8 bits of the warm-up counter become equal to WUCDR, counting is stopped and a
reset is released for the CPU and the peripheral circuits.
WUCDR is initialized to 0x66 after reset release, which makes the warm-up time 0x66 × 29/fc[s].
Note:The clock output from the oscillation circuit is used as the input clock to the warm-up counter.
The warm-up time contains errors because the oscillation frequency is unstable until the oscil-
lation circuit becomes stable.
(2)
When the STOP mode is released
The warm-up counter serves to secure the time after the oscillation is enabled by the hardware before
the oscillation becomes stable at the release of the STOP mode.
The high-frequency clock (fc) or the low-frequency clock (fs), which generates the main system clock
when the STOP mode is activated, is selected as the input clock for frequency division circuit, regardless
of WUCCR<WUCSEL>.
Before the STOP mode is activated, select the division rate of the input clock to the warm-up counter
at WUCCR<WUCDIV> and set the warm-up time at WUCDR.
When the STOP mode is released, the 14-stage counter starts counting the input clock selected in the
frequency division circuit.
When the upper 8 bits of the warm-up counter become equal to WUCDR, counting is stopped and
the operation is restarted by an instruction that follows the STOP mode activation instruction.
Clock that generates the main
system clock when the STOP
mode is activated
WUCCR
<WUCSEL>
WUCCR
<WUCDIV>
Counter input
clock
Warm-up time
fc
Don’t Care
00
fc
26 / fc to 255 x 26 / fc
01
fc / 2
27 / fc to 255 x 27 / fc
10
fc / 22
28 / fc to 255 x 28 / fc
11
fc / 23
29 / fc to 255 x 29 / fc
fs
Don't Care
00
fs
26 / fs to 255 x 26 / fs
01
fs / 2
27 / fs to 255 x 27 / fs
10
fs / 22
28 / fs to 255 x 28 / fs
11
fs / 23
29 / fs to 255 x 29 / fs
Note 1: When the operation is switched to the STOP mode during the warm-up for the oscillation enabled by the software, the
warm-up counter holds the value at the time, and restarts counting after the STOP mode is released. In this case, the
warm-up time at the release of the STOP mode becomes insufficient. Don't switch the operation to the STOP mode during
the warm-up for the oscillation enabled by the software.
TMP89FH42
2. CPU Core
2.3 System clock controller
Page 22
RA004