PIC16C74-20/L Microchip Technology, PIC16C74-20/L Datasheet - Page 132

• Manufacturer Part Number: PIC16C74-20/L
• Description: MICRO CTRL 4K 20MHZ OTP 44PLCC
• Manufacturer: Microchip Technology
• Series: PIC® 16Cr

Specifications of PIC16C74-20/L

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: POR, PWM, WDT
• Number Of I /o: 33
• Program Memory Size: 7KB (4K x 14)
• Program Memory Type: OTP
• Ram Size: 192 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 6 V
• Data Converters: A/D 8x8b
• Oscillator Type: External
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 44-PLCC
• For Use With: DVA16XL441 - ADAPTER DEVICE ICE 44PLCC
• Lead Free Status / RoHS Status: Request inventory verification / Request inventory verification
• Eeprom Size: -

PIC16C7X
14.2.3
Either a prepackaged oscillator can be used or a simple
oscillator circuit with TTL gates can be built. Prepack-
aged oscillators provide a wide operating range and
better stability. A well-designed crystal oscillator will
provide good performance with TTL gates. Two types
of crystal oscillator circuits can be used; one with series
resonance, or one with parallel resonance.
Figure 14-5 shows implementation of a parallel reso-
nant oscillator circuit. The circuit is designed to use the
fundamental frequency of the crystal. The 74AS04
inverter performs the 180-degree phase shift that a par-
allel oscillator requires. The 4.7 k
the negative feedback for stability. The 10 k
ometer biases the 74AS04 in the linear region. This
could be used for external oscillator designs.
FIGURE 14-5: EXTERNAL PARALLEL
Figure 14-6 shows a series resonant oscillator circuit.
This circuit is also designed to use the fundamental fre-
quency of the crystal. The inverter performs a 180-
degree phase shift in a series resonant oscillator cir-
cuit. The 330 k
back to bias the inverters in their linear region.
FIGURE 14-6: EXTERNAL SERIES
DS30390E-page 132
74AS04
330 k
10k
EXTERNAL CRYSTAL OSCILLATOR
CIRCUIT
+5V
0.1 F
XTAL
20 pF
10k
74AS04
XTAL
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
resistors provide the negative feed-
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
4.7k
74AS04
330 k
20 pF
10k
74AS04
74AS04
To Other
Devices
resistor provides
To Other
Devices
PIC16CXX
CLKIN
PIC16CXX
CLKIN
potenti-
14.2.4
For timing insensitive applications the “RC” device
option offers additional cost savings. The RC oscillator
frequency is a function of the supply voltage, the resis-
tor (Rext) and capacitor (Cext) values, and the operat-
ing temperature. In addition to this, the oscillator
frequency will vary from unit to unit due to normal pro-
cess parameter variation. Furthermore, the difference
in lead frame capacitance between package types will
also affect the oscillation frequency, especially for low
Cext values. The user also needs to take into account
variation due to tolerance of external R and C compo-
nents used. Figure 14-7 shows how the R/C combina-
tion is connected to the PIC16CXX. For Rext values
below 2.2 k , the oscillator operation may become
unstable, or stop completely. For very high Rext values
(e.g. 1 M ), the oscillator becomes sensitive to noise,
humidity and leakage. Thus, we recommend to keep
Rext between 3 k and 100 k .
Although the oscillator will operate with no external
capacitor (Cext = 0 pF), we recommend using values
above 20 pF for noise and stability reasons. With no or
small external capacitance, the oscillation frequency
can vary dramatically due to changes in external
capacitances, such as PCB trace capacitance or pack-
age lead frame capacitance.
See characterization data for desired device for RC fre-
quency variation from part to part due to normal pro-
cess variation. The variation is larger for larger R (since
leakage current variation will affect RC frequency more
for large R) and for smaller C (since variation of input
capacitance will affect RC frequency more).
See characterization data for desired device for varia-
tion of oscillator frequency due to V
Cext values as well as frequency variation due to oper-
ating temperature for given R, C, and V
The oscillator frequency, divided by 4, is available on
the OSC2/CLKOUT pin, and can be used for test pur-
poses or to synchronize other logic (see Figure 3-4 for
waveform).
FIGURE 14-7: RC OSCILLATOR MODE
Cext
Rext
V
SS
V
DD
RC OSCILLATOR
Fosc/4
OSC1
OSC2/CLKOUT
1997 Microchip Technology Inc.
DD
DD
for given Rext/
PIC16CXX
values.
Internal
clock