PIC16F877A-I/PT Microchip Technology Inc., PIC16F877A-I/PT Datasheet - Page 126

• 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

PIC16F87X
12.4
A Power-on Reset pulse is generated on-chip when
V
take advantage of the POR, tie the MCLR pin directly
(or through a resistor) to V
external RC components usually needed to create a
Power-on Reset. A maximum rise time for V
ified. See Electrical Specifications for details.
When the device starts normal operation (exits the
RESET condition), device operating parameters (volt-
age, frequency, temperature,...) must be met to ensure
operation. If these conditions are not met, the device
must be held in RESET until the operating conditions
are met. Brown-out Reset may be used to meet the
start-up conditions. For additional information, refer to
Application Note, AN007, “Power-up Trouble Shoot-
ing”, (DS00007).
12.5
The Power-up Timer provides a fixed 72 ms nominal
time-out on power-up only from the POR. The Power-
up Timer operates on an internal RC oscillator. The
chip is kept in RESET as long as the PWRT is active.
The PWRT’s time delay allows V
able level. A configuration bit is provided to enable/dis-
able the PWRT.
The power-up time delay will vary from chip to chip due
to V
parameters for details (T
12.6
The Oscillator Start-up Timer (OST) provides a delay of
1024 oscillator cycles (from OSC1 input) after the
PWRT delay is over (if PWRT is enabled). This helps to
ensure that the crystal oscillator or resonator has
started and stabilized.
The OST time-out is invoked only for XT, LP and HS
modes and only on Power-on Reset or Wake-up from
SLEEP.
TABLE 12-3:
DS30292C-page 124
DD
Oscillator Configuration
DD
rise is detected (in the range of 1.2V - 1.7V). To
, temperature and process variation. See DC
XT, HS, LP
Power-On Reset (POR)
Power-up Timer (PWRT)
Oscillator Start-up Timer (OST)
RC
TIME-OUT IN VARIOUS SITUATIONS
PWRT
, parameter #33).
DD
72 ms + 1024T
DD
. This will eliminate
PWRTE = 0
to rise to an accept-
72 ms
DD
Power-up
OSC
is spec-
PWRTE = 1
1024T
—
OSC
12.7
The configuration bit, BODEN, can enable or disable
the Brown-out Reset circuit. If V
(parameter D005, about 4V) for longer than T
(parameter #35, about 100 S), the brown-out situation
will reset the device. If V
than T
Once the brown-out occurs, the device will remain in
Brown-out Reset until V
Power-up Timer then keeps the device in RESET for
T
below V
cess will restart when V
Power-up Timer Reset. The Power-up Timer is always
enabled when the Brown-out Reset circuit is enabled,
regardless of the state of the PWRT configuration bit.
12.8
On power-up, the time-out sequence is as follows: The
PWRT delay starts (if enabled) when a POR Reset
occurs. Then OST starts counting 1024 oscillator
cycles when PWRT ends (LP, XT, HS). When the OST
ends, the device comes out of RESET.
If MCLR is kept low long enough, the time-outs will
expire. Bringing MCLR high will begin execution imme-
diately. This is useful for testing purposes or to synchro-
nize more than one PIC16F87X device operating in
parallel.
Table 12-5 shows the RESET conditions for the STA-
TUS, PCON and PC registers, while Table 12-6 shows
the RESET conditions for all the registers.
12.9
The Power Control/Status Register, PCON, has up to
two bits depending upon the device.
Bit0 is Brown-out Reset Status bit, BOR. Bit BOR is
unknown on a Power-on Reset. It must then be set by
the user and checked on subsequent RESETS to see if
bit BOR cleared, indicating a BOR occurred. When the
Brown-out Reset is disabled, the state of the BOR bit is
unpredictable and is, therefore, not valid at any time.
Bit1 is POR (Power-on Reset Status bit). It is cleared on
a Power-on Reset and unaffected otherwise. The user
must set this bit following a Power-on Reset.
PWRT
BOR
(parameter #33, about 72mS). If V
BOR
Brown-out Reset (BOR)
Time-out Sequence
Power Control/Status Register
(PCON)
72 ms + 1024T
, a RESET may not occur.
during T
Brown-out
72 ms
PWRT
DD
OSC
DD
DD
2001 Microchip Technology Inc.
, the Brown-out Reset pro-
rises above V
falls below V
rises above V
DD
Wake-up from
falls below V
1024T
SLEEP
DD
BOR
BOR
—
should fall
OSC
BOR
with the
for less
. The
BOR
BOR