PIC17C756-16/SP Microchip Technology, PIC17C756-16/SP Datasheet - Page 15

• Manufacturer Part Number: PIC17C756-16/SP
• Description: MICRO CTRL 16K MEMORY OTP 64SDIP
• Manufacturer: Microchip Technology
• Series: PIC® 17Cr

Specifications of PIC17C756-16/SP

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 16MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 50
• Program Memory Size: 32KB (16K x 16)
• Program Memory Type: OTP
• Ram Size: 902 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 6 V
• Data Converters: A/D 12x10b
• Oscillator Type: External
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 64-SDIP (0.750", 19.05mm)
• Lead Free Status / RoHS Status: Request inventory verification / Request inventory verification
• Eeprom Size: -
• Other names: PIC17C756-16/P

4.0
The internal oscillator circuit is used to generate the
device clock. Four device clock periods generate an
internal instruction clock (T
that the oscillator can operate in. These are selected by
the device configuration bits during device program-
ming. These modes are:
• LF
• XT
• EC
• RC
There are two timers that offer necessary delays on
power-up. One is the Oscillator Start-up Timer (OST),
intended to keep the chip in RESET until the crystal
oscillator is stable. The other is the Power-up Timer
(PWRT), which provides a fixed delay of 96 ms (nomi-
nal) on power-up only, designed to keep the part in
RESET while the power supply stabilizes. With these
two timers on-chip, most applications need no external
reset circuitry.
SLEEP mode is designed to offer a very low current
power-down mode. The user can wake from SLEEP
through external reset, Watchdog Timer Reset or
through an interrupt.
Several oscillator options are made available to allow
the part to fit the application. The RC oscillator option
saves system cost while the LF crystal option saves
power. Configuration bits are used to select various
options.
4.1
4.1.1
The PIC17CXXX can be operated in four different oscil-
lator modes. The user can program two configuration
bits (FOSC1:FOSC0) to select one of these four
modes:
• LF
• XT
• EC
• RC
The main difference between the LF and XT modes is
the gain of the internal inverter of the oscillator circuit
which allows the different frequency ranges.
For more details on the device configuration bits, see
Section 17.0.
1997 Microchip Technology Inc.
ON-CHIP OSCILLATOR
CIRCUIT
Low Frequency (F
Standard Crystal/Resonator Frequency
(2 MHz <= F
External Clock Input
(Default oscillator configuration)
External Resistor/Capacitor
(F
Oscillator Configurations
OSCILLATOR TYPES
OSC
Low Power Crystal
Crystal/Resonator
External Clock Input
Resistor/Capacitor
<= 4 MHz)
OSC
<= 33 MHz)
OSC
CY
). There are four modes
<= 2 MHz)
Preliminary
4.1.2
In XT or LF modes, a crystal or ceramic resonator is
connected to the OSC1/CLKIN and OSC2/CLKOUT
pins
PIC17CXXX oscillator design requires the use of a par-
allel cut crystal. Use of a series cut crystal may give a
frequency out of the crystal manufacturers specifica-
tions.
For frequencies above 20 MHz, it is common for the
crystal to be an overtone mode crystal. Use of overtone
mode crystals require a tank circuit to attenuate the
gain at the fundamental frequency. Figure 4-3 shows
an example circuit.
4.1.2.1
As the device voltage increases from Vss, the oscillator
will start its oscillations. The time required for the oscil-
lator to start oscillating depends on many factors.
These include:
• Crystal / resonator frequency
• Capacitor values used (C1 and C2)
• Device V
• System temperature
• Series resistor value (and type) if used
• Oscillator mode selection of device (which selects
Figure 4-1 shows an example of a typical oscillator /
resonator start-up. The peak-to-peak voltage of the
oscillator waveform can be quite low (less than 50% of
device V
(refer to parameter number D033 and D043 in the elec-
trical specification section).
FIGURE 4-1:
the gain of the internal oscillator inverter)
Crystal Start-up Time
to
DD
CRYSTAL OSCILLATOR / CERAMIC
RESONATORS
DD
establish
OSCILLATOR / RESONATOR START-UP
) when the waveform is centered at V
rise time.
OSCILLATOR / RESONATOR
START-UP
CHARACTERISTICS
oscillation
Time
(Figure 4-2).
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