PIC18F1230 MICROCHIP [Microchip Technology], PIC18F1230 Datasheet - Page 157

• Manufacturer Part Number: PIC18F1230
• Description: 18/20/28-Pin, Enhanced Flash Microcontrollers with nanoWatt Technology, High-Performance PWM and A/D
• Manufacturer: MICROCHIP [Microchip Technology]

14.2.4.1
Since auto-wake-up functions by sensing rising edge
transitions on RX/DT, information with any state
changes before the Stop bit may signal a false End-of-
Character and cause data or framing errors. To work
properly, therefore, the initial characters in the
transmission must be all ‘0’s. This can be 00h (8 bytes)
for standard RS-232 devices or 000h (12 bits) for LIN
bus.
Oscillator start-up time must also be considered,
especially in applications using oscillators with longer
start-up intervals (i.e., XT or HS mode). The Sync
Break (or Wake-up Signal) character must be of
sufficient length and be followed by a sufficient interval
to allow enough time for the selected oscillator to start
and provide proper initialization of the EUSART.
FIGURE 14-8:
FIGURE 14-9:
© 2006 Microchip Technology Inc.
Note 1:
Note 1: The EUSART remains in Idle while the WUE bit is set.
RX/DT Line
RX/DT Line
WUE bit
WUE bit
2:
OSC1
OSC1
RCIF
RCIF
(1)
If the wake-up event requires long oscillator warm-up time, the auto-clear of the WUE bit can occur before the oscillator is ready. This
(2)
sequence should not depend on the presence of Q clocks.
The EUSART remains in Idle while the WUE bit is set.
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
Special Considerations Using
Auto-Wake-up
Bit Set by User
Bit Set by User
Sleep Command Executed
AUTO-WAKE-UP BIT (WUE) TIMINGS DURING NORMAL OPERATION
AUTO-WAKE-UP BIT (WUE) TIMINGS DURING SLEEP
Advance Information
Q1
Sleep Ends
14.2.4.2
The timing of WUE and RCIF events may cause some
confusion when it comes to determining the validity of
received data. As noted, setting the WUE bit places the
EUSART in an Idle mode. The wake-up event causes a
receive interrupt by setting the RCIF bit. The WUE bit is
cleared after this when a rising edge is seen on RX/DT.
The interrupt condition is then cleared by reading the
RCREG register. Ordinarily, the data in RCREG will be
dummy data and should be discarded.
The fact that the WUE bit has been cleared (or is still
set) and the RCIF flag is set should not be used as an
indicator of the integrity of the data in RCREG. Users
should consider implementing a parallel method in
firmware to verify received data integrity.
To assure that no actual data is lost, check the RCIDL
bit to verify that a receive operation is not in process. If
a receive operation is not occurring, the WUE bit may
then be set just prior to entering the Sleep mode.
Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
Cleared Due to User Read of RCREG
Cleared Due to User Read of RCREG
PIC18F1230/1330
Special Considerations Using
the WUE Bit
Note 1
DS39758B-page 155
Auto-Cleared
Auto-Cleared