PIC16F87XA
DS39582B-page 118
2003 Microchip Technology Inc.
FIGURE 10-5:
ASYNCHRONOUS RECEPTION
When setting up an Asynchronous Reception, 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
RCIE.
4.
If 9-bit reception is desired, then set bit RX9.
5.
Enable the reception by setting bit CREN.
6.
Flag bit RCIF will be set when reception is com-
plete and an interrupt will be generated if enable
bit RCIE is set.
7.
Read the RCSTA register to get the ninth bit (if
enabled) and determine if any error occurred
during reception.
8.
Read the 8-bit received data by reading the
RCREG register.
9.
If any error occurred, clear the error by clearing
enable bit CREN.
10. If using interrupts, ensure that GIE and PEIE
(bits 7 and 6) of the INTCON register are set.
TABLE 10-6:
REGISTERS ASSOCIATED WITH ASYNCHRONOUS RECEPTION
Start
bit
bit 7/8
bit 1
bit 0
bit 7/8
bit 0
Stop
bit
Start
bit
Start
bit
bit 7/8
Stop
bit
RX (pin)
Reg
Rcv Buffer Reg
Rcv Shift
Read Rcv
Buffer Reg
RCREG
RCIF
(Interrupt Flag)
OERR bit
CREN
Word 1
RCREG
Word 2
RCREG
Stop
bit
Note:
This timing diagram shows three words appearing on the RX input. The RCREG (Receive Buffer) is read after the third word,
causing the OERR (Overrun Error) bit to be set.
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
TMR0IE
INTE
RBIE
TMR0IF
INTF
R0IF
0000 000x
0000 000u
0Ch
PIR1
PSPIF
(1)
ADIF
RCIF
TXIF
SSPIF
CCP1IF
TMR2IF
TMR1IF
0000 0000
0000 0000
18h
RCSTA
SPEN
RX9
SREN
CREN
—
FERR
OERR
RX9D
0000 -00x
0000 -00x
1Ah
RCREG USART Receive Register
0000 0000
0000 0000
8Ch
PIE1
PSPIE
(1)
ADIE
RCIE
TXIE
SSPIE
CCP1IE
TMR2IE TMR1IE
0000 0000
0000 0000
98h
TXSTA
CSRC
TX9
TXEN
SYNC
—
BRGH
TRMT
TX9D
0000 -010
0000 -010
99h
SPBRG
Baud Rate Generator Register
0000 0000
0000 0000
Legend:
x
= unknown,
-
= unimplemented locations read as ‘
0
’. Shaded cells are not used for asynchronous reception.
Note
1:
Bits PSPIE and PSPIF are reserved on 28-pin devices; always maintain these bits clear.
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