PIC18F1230/1330
2009 Microchip Technology Inc.
DS39758D-page 161
FIGURE 15-7:
ASYNCHRONOUS RECEPTION
TABLE 15-6:
REGISTERS ASSOCIATED WITH ASYNCHRONOUS RECEPTION
15.2.4
AUTO-WAKE-UP ON SYNC
BREAK CHARACTER
During Sleep mode, all clocks to the EUSART are
suspended. Because of this, the Baud Rate Generator
is inactive and a proper byte reception cannot be
performed. The auto-wake-up feature allows the
controller to wake-up due to activity on the RX/DT line
while the EUSART is operating in Asynchronous mode.
The auto-wake-up feature is enabled by setting the
WUE bit (BAUDCON<1>). Once set, the typical receive
sequence on RX/DT is disabled and the EUSART
remains in an Idle state, monitoring for a wake-up event
independent of the CPU mode. A wake-up event
consists of a high-to-low transition on the RX/DT line.
(This coincides with the start of a Sync Break or a
Wake-up Signal character for the LIN/J2602 protocol.)
Following a wake-up event, the module generates an
RCIF
interrupt.
The
interrupt
is
generated
synchronously to the Q clocks in normal operating
is cleared by reading the RCREG register.
The WUE bit is automatically cleared once a low-to-
high transition is observed on the RX line following the
wake-up event. At this point, the EUSART module is in
Idle mode and returns to normal operation. This signals
to the user that the Sync Break event is over.
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset
Values
on Page:
INTCON
GIE/GIEH PEIE/GIEL TMR0IE
INT0IE
RBIE
TMR0IF
INT0IF
RBIF
PIR1
—
ADIF
RCIF
TXIF
CMP2IF
CMP1IF
CMP0IF
TMR1IF
PIE1
—
ADIE
RCIE
TXIE
CMP2IE
CMP1IE
CMP0IE
TMR1IE
IPR1
—
ADIP
RCIP
TXIP
CMP2IP
CMP1IP
CMP0IP
TMR1IP
RCSTA
SPEN
RX9
SREN
CREN
ADDEN
FERR
OERR
RX9D
RCREG
EUSART Receive Register
TXSTA
CSRC
TX9
TXEN
SYNC
SENDB
BRGH
TRMT
TX9D
BAUDCON
ABDOVF
RCIDL
RXDTP
TXCKP
BRG16
—
WUE
ABDEN
SPBRGH
EUSART Baud Rate Generator Register High Byte
SPBRG
EUSART Baud Rate Generator Register Low Byte
Legend:
— = unimplemented locations read as ‘0’. Shaded cells are not used for asynchronous reception.
Start
bit
bit 7/8
bit 1
bit 0
bit 7/8
bit 0
Stop
bit
Start
bit
Start
bit
bit 7/8
Stop
bit
RX (pin)
Rcv Buffer Reg
Rcv Shift Reg
Read Rcv
Buffer Reg
RCREG
RCIF
(Interrupt Flag)
OERR bit
CREN
Word 1
RCREG
Word 2
RCREG
Stop
bit
Note:
This timing diagram shows three words appearing on the RX input. The RCREG (Receive Buffer) is read after the third word causing
the OERR (Overrun) bit to be set.