PIC16F7X7
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 (see Section 11.1 “AUSART
Baud Rate Generator (BRG)”).
7. Load data to the TXREG register (starts
transmission).
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 11-2:
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 11-3:
ASYNCHRONOUS MASTER TRANSMISSION (BACK TO BACK)
Write to TXREG
Word 2
Start bit
Word 1
BRG Output
(Shift Clock)
RC6/TX/CK (pin)
Start bit
Word 2
bit 0
bit 1
Word 1
bit 7/8
bit 0
Stop bit
TXIF bit
(Interrupt Reg. Flag)
Word 1
Transmit Shift Reg.
Word 2
Transmit Shift Reg.
TRMT bit
(Transmit Shift
Reg. Empty Flag)
Note:
This timing diagram shows two consecutive transmissions.
TABLE 11-7: REGISTERS ASSOCIATED WITH ASYNCHRONOUS TRANSMISSION
Value on
all other
Resets
Value on:
POR, BOR
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 INT0IE
RBIE TMR0IF INT0IF
RBIF
0000 000x 0000 000u
(1)
0Ch
PIR1
PSPIF
SPEN
ADIF
RX9
RCIF
TXIF
SSPIF CCP1IF TMR2IF TMR1IF 0000 0000 0000 0000
18h
RCSTA
SREN CREN ADDEN FERR
OERR
RX9D
0000 000x 0000 000x
0000 0000 0000 0000
19h
TXREG AUSART Transmit Data Register
(1)
8Ch
PIE1
PSPIE
CSRC
ADIE
TX9
RCIE
TXIE
SSPIE CCP1IE TMR2IE TMR1IE 0000 0000 0000 0000
98h
TXSTA
TXEN
SYNC
—
BRGH
TRMT
TX9D
0000 -010 0000 -010
0000 0000 0000 0000
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.
2004 Microchip Technology Inc.
DS30498C-page 139
MICROCHIP [ MICROCHIP ]
