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PIC16F87XATI/SP Datasheet - Page 116

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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)
Start Bit
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 2
Word 1
BRG Output
(Shift Clock)
RC6/TX/CK (pin)
Start Bit
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
Bit 6
0Bh, 8Bh,
INTCON
GIE
PEIE
10Bh,18Bh
(1)
0Ch
PIR1
PSPIF
ADIF
18h
RCSTA
SPEN
RX9
19h
TXREG USART Transmit Register
(1)
8Ch
PIE1
PSPIE
ADIE
98h
TXSTA
CSRC
TX9
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.
DS39582C-page 116
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 0
Bit 1
Word 1
Bit 0
Bit 1
Word 1
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
TMR0IE
INTE
RBIE
TMR0IF
INTF
RCIF
TXIF
SSPIF CCP1IF
TMR2IF
SREN
CREN
FERR
OERR
RCIE
TXIE
SSPIE CCP1IE TMR2IE
TXEN
SYNC
BRGH
TRMT
Bit 7/8
Stop Bit
Start Bit
Bit 7/8
Bit 0
Stop Bit
Word 2
Word 2
Transmit Shift Reg.
Value on
Value on:
Bit 0
all other
POR, BOR
Resets
R0IF
0000 000x
0000 000u
TMR1IF
0000 0000
0000 0000
RX9D
0000 -00x
0000 -00x
0000 0000
0000 0000
TMR1IE
0000 0000
0000 0000
TX9D
0000 -010
0000 -010
0000 0000
0000 0000
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