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PIC18F2525/2620/4525/4620

DS39626E-page 214

2008 Microchip Technology Inc.

FIGURE 18-7:

ASYNCHRONOUS RECEPTION

TABLE 18-6:

REGISTERS ASSOCIATED WITH ASYNCHRONOUS RECEPTION

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 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 protocol.)

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.

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

PSPIF(1)

ADIF

RCIF

TXIF

SSPIF

CCP1IF

TMR2IF

TMR1IF

PIE1

PSPIE(1)

ADIE

RCIE

TXIE

SSPIE

CCP1IE

TMR2IE

TMR1IE

IPR1

PSPIP(1)

ADIP

RCIP

TXIP

SSPIP

CCP1IP

TMR2IP

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.

Note 1:

These bits are unimplemented on 28-pin devices and read as ‘0’.

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.

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