PIC16F877-20/P Microchip Technology, PIC16F877-20/P Datasheet - Page 55

• Manufacturer Part Number: PIC16F877-20/P
• Description: IC MCU FLASH 8KX14 EE 40DIP
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F877-20/P

• Core Size: 8-Bit
• Program Memory Size: 14KB (8K x 14)
• Core Processor: PIC
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 33
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 368 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: External
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 40-DIP (0.600", 15.24mm)
• Controller Family/series: PIC16F
• No. Of I/o's: 33
• Eeprom Memory Size: 256Byte
• Ram Memory Size: 368Byte
• Cpu Speed: 20MHz
• No. Of Timers: 3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: 444-1001 - DEMO BOARD FOR PICMICRO MCU
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

3.2.2
3.2.3
1997 Microchip Technology Inc.
Power-up Timer (PWRT)
Oscillator Start-up Timer (OST)
The Power-up Timer provides a nominal 72 ms delay on Power-on Reset (POR) or Brown-out
Reset (BOR), see
operates on a dedicated internal RC oscillator. The device is kept in reset as long as the PWRT
is active. The PWRT delay allows V
configuration bit can enable/disable the Power-up Timer. The Power-up Timer should always be
enabled when Brown-out Reset is enabled. The polarity of the Power-up Timer configuration bit
is now PWRTE = 0 for enabled, while the initial definition of the bit was PWRTE = 1 for enabled.
Since all new devices will use the PWRTE = 0 for enabled, the text will describe the operation for
such devices. Please refer to the individual Data Sheet to ensure the correct polarity for this bit.
The power-up time delay will vary from device to device due to V
variations. See DC parameters for details.
The Oscillator Start-Up Timer (OST) provides a 1024 oscillator cycle delay (from OSC1 input)
after the PWRT delay is over. This ensures that the crystal oscillator or resonator has started and
is stable.
The OST time-out is invoked only for XT, LP and HS modes and only on Power-on Reset,
Brown-out Reset, or wake-up from SLEEP.
The OST counts the oscillator pulses on the OSC1/CLKIN pin. The counter only starts increment-
ing after the amplitude of the signal reaches the oscillator input thresholds. This delay allows the
crystal oscillator or resonator to stabilize before the device exits the OST delay. The length of the
time-out is a function of the crystal/resonator frequency.
Figure 3-4
frequency crystals this start-up time can become quite long. That is because the time it takes the
low frequency oscillator to start oscillating is longer than the power-up timer’s delay. So the time
from when the power-up timer times-out, to when the oscillator starts to oscillate is a dead time.
There is no minimum or maximum time for this dead time ( T
Figure 3-4: Oscillator Start-up Time
Tosc1
T
OST
shows the operation of the OST circuit in conjunction with the power-up timer. For low
= time for the crystal oscillator to react to an oscillation level detectable by the
= 1024T
Oscillator Start-up Timer (OST).
parameter 33
OSC
.
INTERNAL RESET
PWRT TIME_OUT
OST TIME_OUT
Oscillator
in the
MCLR
DD
V
DD
“Electrical Specifications”
to rise to an acceptable level. The power-up timer enable
POR or BOR Trip Point
T
T
PWRT
OSC
Section 3. Reset
1
DEADTIME
T
T
OST
DEADTIME
DD
section. The Power-up Timer
, temperature, and process
).
DS31003A-page 3-5
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