PIC12LF1822T-I/SN Microchip Technology, PIC12LF1822T-I/SN Datasheet - Page 67
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PIC12LF1822T-I/SN
Manufacturer Part Number
PIC12LF1822T-I/SN
Description
3.5 KB Flash, 128 Bytes RAM, 32 MHz Int. Osc, 6 I/0, Enhanced Mid Range Core, Na
Manufacturer
Microchip Technology
Series
PIC® XLP™ 12Fr
Specifications of PIC12LF1822T-I/SN
Core Processor
PIC
Core Size
8-Bit
Speed
32MHz
Connectivity
I²C, LIN, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
6
Program Memory Size
3.5KB (2K x 14)
Program Memory Type
FLASH
Eeprom Size
256 x 8
Ram Size
128 x 8
Voltage - Supply (vcc/vdd)
1.8 V ~ 3.6 V
Data Converters
A/D 4x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
8-SOIC (3.9mm Width)
Processor Series
PIC12LF
Core
PIC
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
PIC12LF1822T-I/SN
Manufacturer:
MICROCHIP
Quantity:
3 900
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5.5
The Fail-Safe Clock Monitor (FSCM) allows the device
to continue operating should the external oscillator fail.
The FSCM can detect oscillator failure any time after
the Oscillator Start-up Timer (OST) has expired. The
FSCM is enabled by setting the FCMEN bit in the
Configuration Word 1. The FSCM is applicable to all
external Oscillator modes (LP, XT, HS, EC, Timer1
Oscillator and RC).
FIGURE 5-9:
5.5.1
The FSCM module detects a failed oscillator by
comparing the external oscillator to the FSCM sample
clock. The sample clock is generated by dividing the
LFINTOSC by 64. See
detector block is a latch. The external clock sets the
latch on each falling edge of the external clock. The
sample clock clears the latch on each rising edge of the
sample clock. A failure is detected when an entire
half-cycle of the sample clock elapses before the
external clock goes low.
5.5.2
When the external clock fails, the FSCM switches the
device clock to an internal clock source and sets the bit
flag OSFIF of the PIR2 register. Setting this flag will
generate an interrupt if the OSFIE bit of the PIE2
register is also set. The device firmware can then take
steps to mitigate the problems that may arise from a
failed clock. The system clock will continue to be
sourced from the internal clock source until the device
firmware successfully restarts the external oscillator
and switches back to external operation.
The internal clock source chosen by the FSCM is
determined by the IRCF<3:0> bits of the OSCCON
register. This allows the internal oscillator to be
configured before a failure occurs.
2010 Microchip Technology Inc.
LFINTOSC
Oscillator
(~32 s)
External
31 kHz
Clock
Sample Clock
Fail-Safe Clock Monitor
FAIL-SAFE DETECTION
FAIL-SAFE OPERATION
(~2 ms)
488 Hz
÷ 64
FSCM BLOCK DIAGRAM
Figure
Clock Monitor
R
S
5-9. Inside the fail
Latch
PIC12F/LF1822/PIC16F/LF1823
Q
Q
Detected
Failure
Clock
Preliminary
5.5.3
The Fail-Safe condition is cleared after a Reset,
executing a SLEEP instruction or changing the SCS bits
of the OSCCON register. When the SCS bits are
changed, the OST is restarted. While the OST is
running, the device continues to operate from the
INTOSC selected in OSCCON. When the OST times
out, the Fail-Safe condition is cleared and the device
will be operating from the external clock source. The
Fail-Safe condition must be cleared before the OSFIF
flag can be cleared.
5.5.4
The FSCM is designed to detect an oscillator failure
after the Oscillator Start-up Timer (OST) has expired.
The OST is used after waking up from Sleep and after
any type of Reset. The OST is not used with the EC or
RC Clock modes so that the FSCM will be active as
soon as the Reset or wake-up has completed. When
the FSCM is enabled, the Two-Speed Start-up is also
enabled. Therefore, the device will always be executing
code while the OST is operating.
Note:
FAIL-SAFE CONDITION CLEARING
RESET OR WAKE-UP FROM SLEEP
Due to the wide range of oscillator start-up
times, the Fail-Safe circuit is not active
during oscillator start-up (i.e., after exiting
Reset or Sleep). After an appropriate
amount of time, the user should check the
Status bits in the OSCSTAT register to
verify the oscillator start-up and that the
system clock switchover has successfully
completed.
DS41413B-page 67
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