PIC16F877A-I/PT Microchip Technology Inc., PIC16F877A-I/PT Datasheet - Page 133

• Manufacturer Part Number: PIC16F877A-I/PT
• Description: 44 PIN, 7 KB FLASH, 368 RAM, 33 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC16F877A-I/PT

• A/d Inputs: 8-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 5 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 33
• Interface: I2C/SPI/USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 44-pin TQFP
• Programmable Memory: 14K Bytes
• Ram Size: 368 Bytes
• Speed: 20 MHz
• Timers: 2-8-bit, 1-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

12.12 Watchdog Timer (WDT)
The Watchdog Timer is a free running on-chip RC oscil-
lator which does not require any external components.
This RC oscillator is separate from the RC oscillator of
the OSC1/CLKIN pin. That means that the WDT will
run, even if the clock on the OSC1/CLKIN and OSC2/
CLKOUT pins of the device has been stopped, for
example, by execution of a SLEEP instruction.
During normal operation, a WDT time-out generates a
device RESET (Watchdog Timer Reset). If the device is
in SLEEP mode, a WDT time-out causes the device to
wake-up and continue with normal operation (Watch-
dog Timer Wake-up). The TO bit in the STATUS regis-
ter will be cleared upon a Watchdog Timer time-out.
The WDT can be permanently disabled by clearing
configuration bit WDTE (Section 12.1).
FIGURE 12-10:
TABLE 12-7:
2007h
81h,181h
Legend: Shaded cells are not used by the Watchdog Timer.
Note 1: See Register 12-1 for operation of these bits.
Address
2001 Microchip Technology Inc.
Note:
Config. bits
PSA and PS2:PS0 are bits in the OPTION_REG register.
OPTION_REG
Name
SUMMARY OF WATCHDOG TIMER REGISTERS
WATCHDOG TIMER BLOCK DIAGRAM
WDT Timer
Enable Bit
WDT
RBPU
From TMR0 Clock Source
(Figure 5-1)
Bit 7
(1)
BODEN
INTEDG
Bit 6
0
1
(1)
PSA
M
U
X
T0CS
Bit 5
CP1
WDT time-out period values may be found in the Elec-
trical Specifications section under parameter #31. Val-
ues for the WDT prescaler (actually a postscaler, but
shared with the Timer0 prescaler) may be assigned
using the OPTION_REG register.
T0SE
Bit 4
CP0
0
Note 1: The CLRWDT and SLEEP instructions
Time-out
8 - to - 1 MUX
MUX
WDT
Postscaler
2: When a CLRWDT instruction is executed
PWRTE
1
clear the WDT and the postscaler, if
assigned to the WDT, and prevent it from
timing out and generating a device
RESET condition.
Bit 3
and the prescaler is assigned to the WDT,
the prescaler count will be cleared, but
the prescaler assignment is not changed.
PSA
8
(1)
PSA
To TMR0 ( Figure 5-1 )
WDTE
Bit 2
PS2
PIC16F87X
PS2:PS0
FOSC1
Bit 1
DS30292C-page 131
PS1
FOSC0
Bit 0
PS0