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Document # 001-20559 Rev. *D
System Resets
30.4
Timing Diagrams
30.4.1
Power On Reset
A Power on Reset (POR) is triggered whenever the supply
voltage is below the POR trip point. POR ends once the sup-
ply voltage rises above this voltage. Refer to the
for more information on the opera-
tion of the POR block.
POR consists of two pieces: an imprecise POR (IPOR) and
a Precision POR (PPOR). “POR” refers to the OR of these
two functions. IPOR has coarser accuracy and its trip point
is typically lower than PPOR’s trip point. PPOR is derived
from a circuit that is calibrated (during boot), for a very accu-
rate location of the POR trip point.
During POR (POR=1), the IMO is powered off for low power
during start up. Once POR de-asserts, the IMO is started
(see
).
POR configures register reset status bits as shown in
. PPOR does not affect the BandGap Trim regis-
ter (BDG_TR), but IPOR does reset this register.
30.4.2
Watchdog Timer Reset
The user has the option to enable the Watchdog Timer
Reset (WDR), by clearing the PORS bit in the CPU_SCR0
register. Once the PORS bit is cleared, the watchdog timer
cannot be disabled. The only exception to this is if a POR/
XRES event takes place, which disables the WDR. Note that
a WDR does not clear the Watchdog timer. See
for details of the Watchdog operation.
When the watchdog timer expires, a watchdog event occurs
resulting in the reset sequence. Some characteristics
unique to the WDR are as follows.
■
PSoC device reset asserts for one cycle of the CLK32K
clock (at its reset state).
■
The IMO is not halted during or after WDR (that is, the
part does not go through a low power phase).
■
CPU operation re-starts one CLK32K cycle after the
internal reset de-asserts (see
How the WDR configures register reset status bits is shown
in
.
Figure 30-2. Key Signals During WDR
WDR
: Reset 1 cycle, then one additional cycle before the CPU reset is released.
IMO PD
IMO (not to scale)
CPU Reset
(Stays low)
Reset
Sleep Timer
0
1
2
CLK32
Содержание PSoC CY8C23533
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