PIC18CXX2
FIGURE 15-2: ASYNCHRONOUS TRANSMISSION
Write to TXREG
Word 1
BRG output
(shift clock)
RC6/TX/CK (pin)
Start Bit
Bit 0
Bit 1
WORD 1
Bit 7/8
Stop Bit
TXIF bit
(Transmit buffer
reg. empty flag)
WORD 1
Transmit Shift Reg
TRMT bit
(Transmit shift
reg. empty flag)
FIGURE 15-3: ASYNCHRONOUS TRANSMISSION (BACK TO BACK)
Write to TXREG
Word 2
Word 1
BRG output
(shift clock)
RC6/TX/CK (pin)
Start Bit
Start Bit
WORD 2
Bit 0
Bit 1
Bit 7/8
Bit 0
Stop Bit
TXIF bit
(interrupt reg. flag)
WORD 1
TRMT bit
(Transmit shift
reg. empty flag)
WORD 1
Transmit Shift Reg.
WORD 2
Transmit Shift Reg.
Note: This timing diagram shows two consecutive transmissions.
TABLE 15-6: REGISTERS ASSOCIATED WITH ASYNCHRONOUS TRANSMISSION
Value on
POR,
BOR
Value on
all other
Resets
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
INTCON GIE/GIEH PEIE/ TMR0IE INT0IE RBIE TMR0IF INT0IF
GIEL
RBIF
0000 000x 0000 000u
PIR1
PSPIF(1)
ADIF
RCIF
RCIE
RCIP
TXIF SSPIF CCP1IF TMR2IF TMR1IF 0000 0000 0000 0000
TXIE SSPIE CCP1IE TMR2IE TMR1IE 0000 0000 0000 0000
TXIP SSPIP CCP1IP TMR2IP TMR1IP 0000 0000 0000 0000
PIE1
PSPIE(1) ADIE
PSPIP(1) ADIP
IPR1
RCSTA
TXREG
TXSTA
SPBRG
SPEN
USART Transmit Register
CSRC TX9 TXEN SYNC
Baud Rate Generator Register
RX9
SREN CREN
—
FERR
OERR
RX9D 0000 -00x 0000 -00x
0000 0000 0000 0000
—
BRGH
TRMT
TX9D
0000 -010 0000 -010
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 PIC18C2X2 devices. Always maintain these bits
clear.
DS39026B-page 158
Preliminary
7/99 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
