PIC18F4580T-I/PT Microchip Technology, PIC18F4580T-I/PT Datasheet - Page 339

• Manufacturer Part Number: PIC18F4580T-I/PT
• Description: IC PIC MCU FLASH 16KX16 44TQFP
• Manufacturer: Microchip Technology
• Series: PIC® 18Fr

Specifications of PIC18F4580T-I/PT

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 40MHz
• Connectivity: CAN, I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, HLVD, POR, PWM, WDT
• Number Of I /o: 36
• Program Memory Size: 32KB (16K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 1.5K x 8
• Voltage - Supply (vcc/vdd): 4.2 V ~ 5.5 V
• Data Converters: A/D 11x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-TQFP, 44-VQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

24.9.1
The microcontroller clock frequency generated from a
PLL circuit is subject to a jitter, also defined as Phase
Jitter or Phase Skew. For its PIC18 Enhanced micro-
controllers, Microchip specifies phase jitter (P
being 2% (Gaussian distribution, within 3 standard
deviations, see parameter F13 in Table 28-7) and Total
Jitter (T
FIGURE 24-5:
Once these considerations are taken into account, it is
possible to show that the relation between the jitter and
the total frequency error can be defined as:
where jitter is expressed in terms of time and NBT is the
Nominal Bit Time.
© 2009 Microchip Technology Inc.
jitter
Nominal Clock
Clock with Jitter
CAN Bit Time
with Jitter
) as being 2*P
EXTERNAL CLOCK, INTERNAL
CLOCK AND MEASURABLE JITTER
IN HS-PLL BASED OSCILLATORS
Δf
=
----------------------- -
10 NBT
T
×
EFFECTS OF PHASE JITTER ON THE MICROCONTROLLER CLOCK
AND CAN BIT TIME
jitter
jitter
.
=
----------------------- -
10 NBT
2 P
×
×
jitter
PIC18F2480/2580/4480/4580
jitter
) as
Phase Skew (Jitter)
CAN Bit Jitter
The CAN protocol uses a bit-stuffing technique that
inserts a bit of a given polarity following five bits with the
opposite polarity. This gives a total of 10 bits transmit-
ted without re-synchronization (compensation for jitter
or phase error).
Given the random nature of the jitter error added, it can
be shown that the total error caused by the jitter tends
to cancel itself over time. For a period of 10 bits, it is
necessary to add only two jitter intervals to correct for
jitter-induced error: one interval in the beginning of the
10-bit period and another at the end. The overall effect
is shown in Figure 24-5.
For example, assume a CAN bit rate of 125 Kb/s, which
gives an NBT of 8 µs. For a 16 MHz clock generated
from a 4x PLL, the jitter at this clock frequency is:
and resultant frequency error is:
2
-------------------------------------- -
10
×
2%
(
×
1.25
(
8
×
×10
-------------------
16 MHz
×10
6 –
1
–
9
)
)
=
=
3.125
-----------------
16
0.02
×10
×10
6
–
5
=
DS39637D-page 339
=
1.25ns
0.0031%