
2003 Microchip Technology Inc.
DS30569B-page 67
PIC16F870/871
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,
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.
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.
FIGURE 9-2:
ASYNCHRONOUS MASTER TRANSMISSION
FIGURE 9-3:
ASYNCHRONOUS MASTER TRANSMISSION (BACK TO BACK)
TABLE 9-5:
REGISTERS ASSOCIATED WITH ASYNCHRONOUS TRANSMISSION
Address
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
0Bh, 8Bh,
10Bh,18Bh
INTCON
GIE
PEIE
T0IE
INTE
RBIE
T0IF
INTF
R0IF
0000 000x
0000 000u
0Ch
PIR1
PSPIF(1)
ADIF
RCIF
TXIF
—
CCP1IF
TMR2IF
TMR1IF
0000 -000
18h
RCSTA
SPEN
RX9
SREN
CREN
—
FERR
OERR
RX9D
0000 -00x
19h
TXREG
USART Transmit Register
0000 0000
8Ch
PIE1
PSPIE(1)
ADIE
RCIE
TXIE
—
CCP1IE
TMR2IE
TMR1IE
0000 -000
98h
TXSTA
CSRC
TX9
TXEN
SYNC
—
BRGH
TRMT
TX9D
0000 -010
99h
SPBRG
Baud Rate Generator Register
0000 0000
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 the PIC16F870; always maintain these bits clear.
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.