Microchip Technology PIC16F87XA Datasheet page 118

PIC16F87XA
When setting up an Asynchronous Transmission,
follow these steps:
1. Initialize the SPBRG register for the appropriate
baud rate. If a high-speed baud rate is desired,
set bit BRGH (Section 10.1 "USART Baud
Rate Generator (BRG)").
2. Enable the asynchronous serial port by clearing
bit SYNC and setting bit SPEN.
3. If interrupts are desired, then set enable bit TXIE.
4. If 9-bit transmission is desired, then set transmit
bit TX9.
FIGURE 10-2: ASYNCHRONOUS MASTER TRANSMISSION
Write to TXREG
Word 1
BRG Output
(Shift Clock)
RC6/TX/CK (pin)
TXIF bit
(Transmit Buffer
Reg. Empty Flag)
Word 1
TRMT bit
Transmit Shift Reg
(Transmit Shift
Reg. Empty Flag)
FIGURE 10-3: ASYNCHRONOUS MASTER TRANSMISSION (BACK TO BACK)
Write to TXREG
Word 1
BRG Output
(Shift Clock)
RC6/TX/CK (pin)
TXIF bit
(Interrupt Reg. Flag)
TRMT bit
Word 1
(Transmit Shift
Transmit Shift Reg.
Reg. Empty Flag)
Note: This timing diagram shows two consecutive transmissions.
TABLE 10-5: REGISTERS ASSOCIATED WITH ASYNCHRONOUS TRANSMISSION
Address Name Bit 7
0Bh, 8Bh, INTCON GIE
10Bh,18Bh
0Ch PIR1 PSPIF
18h RCSTA SPEN
19h TXREG USART Transmit Register
8Ch PIE1 PSPIE
98h TXSTA CSRC
99h SPBRG Baud Rate Generator Register
Legend: x = unknown, - = unimplemented locations read as '0'. Shaded cells are not used for asynchronous transmission.
Note 1: Bits PSPIE and PSPIF are reserved on 28-pin devices; always maintain these bits clear.
DS39582B-page 116
http://www.xinpian.net
Start Bit Bit 0
Word 2
Start Bit
Bit 0
Bit 6 Bit 5 Bit 4
PEIE TMR0IE INTE
(1)
ADIF RCIF TXIF
RX9 SREN CREN
(1)
ADIE RCIE TXIE
TX9 TXEN SYNC
提供单片机解密、IC解密、芯片解密业务
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).
8. If using interrupts, ensure that GIE and PEIE
(bits 7 and 6) of the INTCON register are set.
Bit 1 Bit 7/8
Word 1
Bit 1
Bit 7/8
Word 1
Word 2
Transmit Shift Reg.
Bit 3 Bit 2 Bit 1
RBIE TMR0IF INTF
SSPIF CCP1IF TMR2IF TMR1IF
— FERR OERR
SSPIE CCP1IE TMR2IE TMR1IE
— BRGH TRMT
Stop Bit
Start Bit
Bit 0
Stop Bit
Word 2
Value on
Value on:
Bit 0 all other
POR, BOR
Resets
R0IF
0000 000x 0000 000u
0000 0000 0000 0000
RX9D
0000 -00x 0000 -00x
0000 0000 0000 0000
0000 0000 0000 0000
TX9D
0000 -010 0000 -010
0000 0000 0000 0000
 2003 Microchip Technology Inc.
010-62245566 13810019655