
2002 Microchip Technology Inc.
Preliminary
DS30485A-page 173
PIC18FXX39
FIGURE 17-2:
ASYNCHRONOUS TRANSMISSION
FIGURE 17-3:
ASYNCHRONOUS TRANSMISSION (BACK TO BACK)
TABLE 17-6:
REGISTERS ASSOCIATED WITH ASYNCHRONOUS TRANSMISSION
Word 1
STOP bit
Word 1
Transmit Shift Reg
START bit
bit 0
bit 1
bit 7/8
Write to TXREG
Word 1
BRG Output
(Shift Clock)
RC6/TX/CK (pin)
TXIF bit
(Transmit Buffer
Reg. Empty Flag)
TRMT bit
(Transmit Shift
Reg. Empty Flag)
Transmit Shift Reg.
Write to TXREG
BRG Output
(Shift Clock)
RC6/TX/CK (pin)
TXIF bit
(Interrupt Reg. Flag)
TRMT bit
(Transmit Shift
Reg. Empty Flag)
Word 1
Word 2
Word 1
Word 2
START bit
STOP bit
START bit
Transmit Shift Reg.
Word 1
Word 2
bit 0
bit 1
bit 7/8
bit 0
Note:
This timing diagram shows two consecutive transmissions.
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(1)
ADIF
RCIF
TXIF
SSPIF
—
TMR2IF TMR1IF 0000 0000 0000 0000
PIE1
PSPIE(1)
ADIE
RCIE
TXIE
SSPIE
—
TMR2IE TMR1IE 0000 0000 0000 0000
IPR1
PSPIP(1)
ADIP
RCIP
TXIP
SSPIP
—
TMR2IP TMR1IP 0000 0000 0000 0000
RCSTA
SPEN
RX9
SREN
CREN ADDEN FERR
OERR
RX9D
0000 -00x 0000 -00x
TXREG USART Transmit Register
0000 0000 0000 0000
TXSTA
CSRC
TX9
TXEN
SYNC
—
BRGH
TRMT
TX9D
0000 -010 0000 -010
SPBRG Baud Rate Generator Register
0000 0000 0000 0000
Legend: x = unknown, - = unimplemented locations read as '0'.
Shaded cells are not used for Asynchronous Transmission.
Note 1: The PSPIF, PSPIE and PSPIP bits are reserved on the PIC18F2X39 devices; always maintain these bits
clear.