PIC16F87XA
When setting up an Asynchronous Transmission,
follow these steps:
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.
1. Initialize the SPBRG register for the appropriate
baud rate. If a high speed baud rate is desired,
set bit BRGH (Section 10.1).
7. Load data to the TXREG register (starts trans-
mission).
2. Enable the asynchronous serial port by clearing
bit SYNC and setting bit SPEN.
8. If using interrupts, ensure that GIE and PEIE
(bits 7 and 6) of the INTCON register are set.
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)
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 10-3:
ASYNCHRONOUS MASTER 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
Word 1
Bit 7/8
Bit 0
STOP Bit
TXIF bit
(Interrupt Reg. Flag)
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 10-5: REGISTERS ASSOCIATED WITH ASYNCHRONOUS TRANSMISSION
Value on:
POR,
BOR
Value on
all other
RESETS
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0Bh, 8Bh, INTCON
10Bh,18Bh
GIE
PEIE TMR0IE INTE
RBIE TMR0IF
INTF
R0IF
0000 000x 0000 000u
(1)
0Ch
18h
19h
8Ch
98h
99h
PIR1
PSPIF
SPEN
ADIF
RX9
RCIF
TXIF
SSPIF CCP1IF TMR2IF TMR1IF 0000 0000 0000 0000
RCSTA
SREN CREN
—
FERR
OERR
RX9D
0000 -00x 0000 -00x
0000 0000 0000 0000
TXREG USART Transmit Register
(1)
PIE1
PSPIE
CSRC
ADIE
TX9
RCIE
TXIE SSPIE CCP1IE TMR2IE TMR1IE 0000 0000 0000 0000
TXSTA
TXEN
SYNC
—
BRGH
TRMT
TX9D
0000 -010 0000 -010
0000 0000 0000 0000
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.
DS39582A-page 114
AdvanceInformation
2001 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
