PIC16F87-I/SS Microchip Technology, PIC16F87-I/SS Datasheet - Page 143

• Manufacturer Part Number: PIC16F87-I/SS
• Description: IC MCU FLASH 4KX14 EEPROM 20SSOP
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F87-I/SS

• Program Memory Type: FLASH
• Program Memory Size: 7KB (4K x 14)
• Package / Case: 20-SSOP
• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 16
• Eeprom Size: 256 x 8
• Ram Size: 368 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Processor Series: PIC16F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 368 B
• Interface Type: SSP/USART
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 16
• Number Of Timers: 3
• Operating Supply Voltage: 2 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: 52715-96, 52716-328, 52717-734
• Development Tools By Supplier: PG164130, DV164035, DV244005, DV164005, PG164120, ICE2000, DM163014
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 10 bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: XLT20SS-1 - SOCKET TRANSITION 18DIP 20SSOPAC164307 - MODULE SKT FOR PM3 28SSOP
• Data Converters: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

15.12 Watchdog Timer (WDT)
For PIC16F87/88 devices, the WDT has been modified
from previous PIC16 devices. The new WDT is code
and functionally backward compatible with previous
PIC16 WDT modules, and allows the user to have a
scaler value for the WDT and TMR0 at the same time.
In addition, the WDT time-out value can be extended to
268 seconds, using the prescaler with the postscaler
when PSA is set to ‘1’.
15.12.1
The WDT derives its time base from the 31.25 kHz
INTRC. The value of WDTCON is ‘---0 1000’ on all
RESETS. This gives a nominal time base of 16.38 ms,
which is compatible with the time base generated with
previous PIC16 microcontroller versions.
A new prescaler has been added to the path between
the internal RC and the multiplexors used to select the
path for the WDT. This prescaler is 16 bits and can be
programmed to divide the internal RC by 128 to 65536,
giving the time base used for the WDT a nominal range
of 1 ms to 2.097s.
FIGURE 15-8:
 2003 Microchip Technology Inc.
Note:
INTRC Clock
31.25 kHz
WDT OSCILLATOR
When the OST is invoked, the WDT is held
in RESET, because the WDT ripple
counter is used by the OST to perform the
oscillator delay count. When the OST
count has expired, the WDT will begin
counting (if enabled).
WATCHDOG TIMER BLOCK DIAGRAM
16-bit Programmable Prescaler WDT
WDTEN from Configuration Word
SWDTEN from WDTCON
WDTPS<3:0>
Preliminary
From TMR0 Clock Source
15.12.2
The WDTEN bit is located in Configuration Word 1 and
when this bit is set, the WDT runs continuously.
The SWDTEN bit is in the WDTCON register. When the
WDTEN bit in the Configuration Word 1 register is set,
the SWDTEN bit has no effect. If WDTEN is clear, then
the SWDTEN bit can be used to enable and disable the
WDT. Setting the bit will enable it and clearing the bit
will disable it.
The PSA and PS<2:0> bits (OPTION_REG) have the
same function as in previous versions of the PIC16
family of microcontrollers.
0
1
WDT CONTROL
PSA
PIC16F87/88
WDT Time-out
0
Postscaler
1
8
DS30487B-page 141
PSA
TO TMR0
PS<2:0>