PIC18F2420/2520/4420/4520
FIGURE 18-7:
ASYNCHRONOUS RECEPTION
Start
bit
Start
bit
Start
bit
RX (pin)
Stop
bit
Stop
bit
Stop
bit
bit 0 bit 1
bit 7/8
bit 0
bit 7/8
bit 7/8
Rcv Shift Reg
Rcv Buffer Reg
Word 2
RCREG
Word 1
RCREG
Read Rcv
Buffer Reg
RCREG
RCIF
(Interrupt Flag)
OERR bit
CREN
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.
TABLE 18-6: REGISTERS ASSOCIATED WITH ASYNCHRONOUS RECEPTION
Reset
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Values
on page
INTCON
PIR1
GIE/GIEH PEIE/GIEL TMR0IE
INT0IE
TXIF
RBIE
SSPIF
SSPIE
SSPIP
ADDEN
TMR0IF
INT0IF
RBIF
49
52
52
52
51
51
51
51
51
51
PSPIF(1)
PSPIE(1)
PSPIP(1)
SPEN
ADIF
ADIE
ADIP
RX9
RCIF
RCIE
RCIP
SREN
CCP1IF TMR2IF TMR1IF
CCP1IE TMR2IE TMR1IE
CCP1IP TMR2IP TMR1IP
PIE1
TXIE
IPR1
TXIP
RCSTA
RCREG
TXSTA
CREN
FERR
OERR
RX9D
EUSART Receive Register
CSRC
TX9
TXEN
SYNC
SENDB
BRG16
BRGH
—
TRMT
WUE
TX9D
BAUDCON ABDOVF
RCIDL
RXDTP
TXCKP
ABDEN
SPBRGH
SPBRG
EUSART Baud Rate Generator Register High Byte
EUSART Baud Rate Generator Register Low Byte
Legend: — = unimplemented locations read as ‘0’. Shaded cells are not used for asynchronous reception.
Note 1: Reserved in 28-pin devices; always maintain these bits clear.
Following a wake-up event, the module generates an
RCIF interrupt. The interrupt is generated synchro-
nously to the Q clocks in normal operating modes
(Figure 18-8) and asynchronously, if the device is in
Sleep mode (Figure 18-9). The interrupt condition is
cleared by reading the RCREG register.
18.2.4
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 per-
formed. 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 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.
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 con-
sists 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 protocol.)
DS39631E-page 214
© 2008 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
