
2004 Microchip Technology Inc.
DS30491C-page 241
PIC18F6585/8585/6680/8680
To set up an asynchronous transmission:
1.
Initialize the SPBRG register for the appropriate
baud rate. If a high-speed baud rate is desired,
2.
Enable the asynchronous serial port by clearing
bit SYNC and setting bit SPEN.
3.
If interrupts are desired, set enable bit TXIE.
4.
If 9-bit transmission is desired, set transmit bit
TX9. Can be used as address/data bit.
5.
Enable the transmission by setting bit TXEN
which will also set bit TXIF.
6.
If 9-bit transmission is selected, the ninth bit
should be loaded in bit TX9D.
7.
Load data to the TXREG register (starts
transmission).
If using interrupts, ensure that the GIE and PEIE bits in
the INTCON register (INTCON<7:6>) are set.
FIGURE 18-6:
ASYNCHRONOUS RECEPTION
TABLE 18-6:
REGISTERS ASSOCIATED WITH 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)
Reg
Rcv Buffer Reg
Rcv Shift
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.
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on
POR, BOR
Value on
all other
Resets
INTCON
GIE/GIEH
PEIE/GIEL
TMR0IE
INT0IE
RBIE
TMR0IF
INT0IF
RBIF
0000 000x
0000 000u
PIR1
PSPIF
ADIF
RCIF
TXIF
SSPIF
CCP1IF
TMR2IF
TMR1IF
0000 0000
PIE1
PSPIE
ADIE
RCIE
TXIE
SSPIE
CCP1IE
TMR2IE
TMR1IE
0000 0000
IPR1
PSPIP
ADIP
RCIP
TXIP
SSPIP
CCP1IP
TMR2IP
TMR1IP
1111 1111
RCSTA
SPEN
RX9
SREN
CREN
ADDEN
FERR
OERR
RX9D
0000 000x
RCREG
USART Receive Register
0000 0000
TXSTA
CSRC
TX9
TXEN
SYNC
SENDB
BRGH
TRMT
TX9D
0000 0010
BAUDCON
—
RCIDL
—
SCKP
BRG16
—
WUE
ABDEN
-1-1 0-00
SPBRGH
Baud Rate Generator Register, High Byte
0000 0000
SPBRG
Baud Rate Generator Register, Low Byte
0000 0000
Legend:
x
= unknown, – = unimplemented locations read as ‘0’. Shaded cells are not used for asynchronous reception.