PRELIMINARY
PSoC®3: CY8C38 Family Data Sheet
Document Number: 001-11729 Rev. *I
Page 28 of 100
6.3 Reset
CY8C38 has multiple internal and external reset sources
available. The reset sources are:
Power source monitoring - The analog and digital power
voltages, Vdda, Vddd, Vcca, and Vccd are monitored in several
different modes during power up, normal operation, and sleep
and hibernate states. If any of the voltages goes outside prede-
termined ranges then a reset is generated. The monitors are
programmable to generate an interrupt to the processor under
certain conditions before reaching the reset thresholds.
External - The device can be reset from an external source by
pulling the reset pin (XRES) low. The XRES pin includes an
internal pull up to Vddio1. Vddd, Vdda, and Vddio1 must all
have voltage applied before the part comes out of reset.
Watchdog timer - A watchdog timer monitors the execution of
instructions by the processor. If the watchdog timer is not reset
by firmware within a certain period of time, the watchdog timer
generates a reset.
Software - The device can be reset under program control.
Figure 6-5. Resets
The term device reset indicates that the processor as well as
analog and digital peripherals and registers are reset.
A reset status register holds the source of the most recent reset
or power voltage monitoring interrupt. The program may
examine this register to detect and report exception conditions.
This register is cleared after a power on reset.
6.3.1 Reset Sources
6.3.1.1
Power Voltage Level Monitors
IPOR - Initial Power on Reset
At initial power on, IPOR monitors the power voltages Vddd
and Vdda, both directly at the pins and at the outputs of the
corresponding internal regulators. The trip level is not precise.
It is set to a voltage below the lowest specified operating volt-
age but high enough for the internal circuits to be reset and to
hold their reset state. The monitor generates a reset pulse that
is at least 100 ns wide. It may be much wider if one or more of
the voltages ramps up slowly.
To save power the IPOR circuit is disabled when the internal
digital supply is stable. Voltage supervision is then handed off
to the precise low voltage reset (PRES) circuit. When the volt-
age is high enough for PRES to release, the IMO starts.
PRES - Precise Low Voltage Reset
This circuit monitors the outputs of the analog and digital inter-
nal regulators after power up. The regulator outputs are com-
pared to a precise reference voltage of 1.6V ±0.02V. The re-
sponse to a PRES trip is identical to an IPOR reset.
In normal operating mode, the program cannot disable the dig-
ital PRES circuit. The analog regulator can be disabled, which
also disables the analog portion of the PRES. The PRES cir-
cuit is disabled automatically during sleep and hibernate
modes, with one exception: During sleep mode the regulators
are periodically activated (buzzed) to provide supervisory ser-
vices and to reduce wakeup time. At these times the PRES
circuit is also buzzed to allow periodic voltage monitoring.
HRES - Hibernate/Sleep Low Voltage Reset
This circuit monitors internal voltage and issues a reset if the
voltage drops below a point where state information may be
lost. The response to a HRES trip is identical to an IPOR reset.
This circuit is ultra low power. It is enabled at all times but its
output only causes a reset when the device is in hibernate or
sleep mode.
ALVI, DLVI, AHVI - Analog/Digital Low Voltage Interrupt, Analog
High Voltage Interrupt
Interrupt circuits are available to detect when Vdda and Vddd
go outside a voltage range. For AHVI, Vdda is compared to a
fixed trip level. For ALVI and DLVI, Vdda and Vddd are com-
pared to trip levels that are programmable, as listed in
Table 6-5.
The monitors are disabled until after IPOR. During sleep mode
these circuits are periodically activated (buzzed). If an interrupt
occurs during buzzing then the system first enters its wake up
sequence. The interrupt is then recognized and may be ser-
viced.
Reset
Controller
Watchdog
Timer
External
Reset
Power
Voltage
Level
Monitors
Software
Reset
Register
Vddd Vdda
Reset
Pin
System
Reset
Processor
Interrupt
Table 6-5. Analog/Digital Low Voltage Interrupt, Analog High
Voltage Interrupt
Interrupt
Supply
Normal
Voltage
Range
Available Trip
Settings
Accuracy
DLVI
Vddd
1.71V-5.5V 1.70V-5.45V in
250 mV
increments
±2%
ALVI
Vdda
1.71V-5.5V 1.70V-5.45V in
250 mV
increments
±2%
AHVI
Vdda
1.71V-5.5V 5.75V
±2%
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