PIC18LF6310-I/PT Microchip Technology, PIC18LF6310-I/PT Datasheet - Page 293

• Manufacturer Part Number: PIC18LF6310-I/PT
• Description: IC PIC MCU FLASH 4KX16 64TQFP
• Manufacturer: Microchip Technology
• Series: PIC® 18Fr

Specifications of PIC18LF6310-I/PT

• Core Size: 8-Bit
• Program Memory Size: 8KB (4K x 16)
• Oscillator Type: Internal
• Core Processor: PIC
• Speed: 40MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, HLVD, POR, PWM, WDT
• Number Of I /o: 54
• Program Memory Type: FLASH
• Ram Size: 768 x 8
• Voltage - Supply (vcc/vdd): 2 V ~ 5.5 V
• Data Converters: A/D 12x10b
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 64-TFQFP
• Controller Family/series: PIC18
• No. Of I/o's: 54
• Ram Memory Size: 768Byte
• Cpu Speed: 40MHz
• No. Of Timers: 4
• No. Of Pwm: RoHS Compliant
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

24.4
The Fail-Safe Clock Monitor (FSCM) allows the
microcontroller to continue operation in the event of an
external oscillator failure by automatically switching the
device clock to the internal oscillator block. The FSCM
function
Configuration bit.
When FSCM is enabled, the INTRC oscillator runs at
all times to monitor clocks to peripherals and provide a
backup clock in the event of a clock failure. Clock
monitoring (shown in
creating a sample clock signal, which is the INTRC
output divided by 64. This allows ample time between
FSCM sample clocks for a peripheral clock edge to
occur. The peripheral device clock and the sample
clock are presented as inputs to the Clock Monitor latch
(CM). The CM is set on the falling edge of the device
clock source, but cleared on the rising edge of the
sample clock.
FIGURE 24-3:
Clock failure is tested for on the falling edge of the
sample clock. If a sample clock falling edge occurs
while CM is still set, a clock failure has been detected
(Figure
• the FSCM generates an oscillator fail interrupt by
• the device clock source is switched to the internal
• the WDT is reset.
During switchover, the postscaler frequency from the
internal oscillator block may not be sufficiently stable for
timing-sensitive applications. In these cases, it may be
desirable to select another clock configuration and enter
an alternate power-managed mode. This can be done to
attempt a partial recovery or execute a controlled shut-
down. See
Modes”
for Using Two-Speed Start-up”
 2010 Microchip Technology Inc.
setting bit, OSCFIF (PIR2<7>);
oscillator block (OSCCON is not updated to show
the current clock source – this is the Fail-Safe
condition); and
Peripheral
Source
(32 s)
INTRC
Clock
24-4). This causes the following:
and
Fail-Safe Clock Monitor
is
Section 4.1.2 “Entering Power-Managed
Section 24.3.1 “Special Considerations
(2.048 ms)
enabled
488 Hz
÷ 64
Figure
FSCM BLOCK DIAGRAM
Clock Monitor (CM)
(edge-triggered)
by
24-3) is accomplished by
C
S
Latch
setting
for more details.
Q
Q
the
Detected
PIC18F6310/6410/8310/8410
Failure
Clock
FCMEN
To use a higher clock speed on wake-up, the INTOSC
or postscaler clock sources can be selected to provide
a higher clock speed by setting bits, IRCF<2:0>, imme-
diately after Reset. For wake-ups from Sleep, the
INTOSC or postscaler clock sources can be selected
by setting the IRCF<2:0> bits prior to entering Sleep
mode.
The FSCM will detect failures of the primary or second-
ary clock sources only. If the internal oscillator block
fails, no failure would be detected, nor would any action
be possible.
24.4.1
Both the FSCM and the WDT are clocked by the
INTRC oscillator. Since the WDT operates with a
separate divider and counter, disabling the WDT has
no effect on the operation of the INTRC oscillator when
the FSCM is enabled.
As already noted, the clock source is switched to the
INTOSC clock when a clock failure is detected.
Depending on the frequency selected by the
IRCF<2:0> bits, this may mean a substantial change in
the speed of code execution. If the WDT is enabled
with a small prescale value, a decrease in clock speed
allows a WDT time-out to occur and a subsequent
device Reset. For this reason, Fail-Safe Clock events
also reset the WDT and postscaler, allowing it to start
timing from when execution speed was changed, and
decreasing the likelihood of an erroneous time-out.
24.4.2
The Fail-Safe condition is terminated by either a device
Reset or by entering a power-managed mode. On
Reset, the controller starts the primary clock source
specified in Configuration Register 1H (with any
required start-up delays that are required for the
oscillator mode, such as the OST or PLL timer). The
INTOSC multiplexer provides the device clock until the
primary clock source becomes ready (similar to a
Two-Speed Start-up). The clock source is then
switched to the primary clock (indicated by the OSTS
bit in the OSCCON register becoming set). The
Fail-Safe Clock Monitor then resumes monitoring the
peripheral clock.
The primary clock source may never become ready
during start-up. In this case, operation is clocked by the
INTOSC multiplexer. The OSCCON register will remain
in its Reset state until a power-managed mode is
entered.
FSCM AND THE WATCHDOG TIMER
EXITING FAIL-SAFE OPERATION
DS39635C-page 293