PIC16F818-I/P Microchip Technology, PIC16F818-I/P Datasheet - Page 40

• Manufacturer Part Number: PIC16F818-I/P
• Description: IC MCU FLASH 1KX14 18-DIP
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F818-I/P

• Program Memory Type: FLASH
• Program Memory Size: 1.75KB (1K x 14)
• Package / Case: 18-DIP (0.300", 7.62mm)
• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 16
• Eeprom Size: 128 x 8
• Ram Size: 128 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Data Converters: A/D 5x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Processor Series: PIC16F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 128 B
• Interface Type: I2C/SPI/SSP
• 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: Through Hole
• 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: 5-ch x 10-bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: ACICE0202 - ADAPTER MPLABICE 18P 300 MILAC164010 - MODULE SKT PROMATEII DIP/SOIC
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

PICmicro MID-RANGE MCU FAMILY
2.3.3.1.1
2.3.4
DS31002A-page 2-10
Start-up
External Clock Input
The OSC2 signal should be a nice clean sine wave that easily spans the input minimum and max-
imum of the clock input pin (4V to 5V peak to peak for a 5V V
to set this is to again test the circuit at the minimum temperature and maximum V
design will be expected to perform in, then look at the output. This should be the maximum ampli-
tude of the clock output. If there is clipping or the sine wave is squashing near V
the top and bottom, and increasing load capacitors will risk too much current through the crystal
or push the value too far from the manufacturer’s load specification, then add a trimpot between
the output pin and C2, and adjust it until the sine wave is clean. Keeping it fairly close to maximum
amplitude at the low temperature and high V
amplitude the crystal will see and prevent overdriving. A series resistor, Rs, of the closest stan-
dard value, can now be inserted in place of the trimpot. If Rs is too high, perhaps more than
20k ohms, the input will be too isolated from the output, making the clock more susceptible to
noise. If you find a value this high is needed to prevent overdriving the crystal, try increasing C2
to compensate. Try to get a combination where Rs is around 10k or less, and load capacitance
is not too far from the 20 pF or 32 pF manufacturer specification.
The most difficult time for the oscillator to start-up is when waking up from sleep. This is because
the load capacitors have both partially charged to some quiescent value, and phase differential
at wake-up is minimal. Thus, more time is required to achieve stable oscillation. Remember also
that low voltage, high temperatures, and the lower frequency clock modes also impose limitations
on loop gain, which in turn affects start-up. Each of the following factors makes thing worse:
• a low frequency design (with its low gain clock mode)
• a quiet environment (such as a battery operated device)
• operating outside the noisy RF area (such as in a shielded box)
• low voltage
• high temperature
• waking up from sleep.
Noise actually helps a design for oscillator start-up, since it helps kick start the oscillator.
If the PICmicro’s internal oscillator is not being used, and the device will be driven from an exter-
nal clock, be sure to set the oscillator mode to one of the crystal modes (LP, XT, or HS). That is,
something other than one of the RC modes, since RC mode will fight with the injected input. Ide-
ally you would select the mode that corresponds to the frequency injected, but this is of less
importance here since the clock is only driving its internal logic, and not a crystal loop circuit. It
may be possible to select a clock mode lower than would be needed by an oscillator circuit, and
thereby save some of the power that would be used exercising the inverting amplifier. Make sure
the OSC2 signal amplitude covers the needed logic thresholds of the device.
Figure 2-3: External Device Clock Input Operation (HS, XT or LP Oscillator Modes)
Note 1: A resistor to ground may be used to reduce system noise.
This may increase system current.
external system
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OSC2
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