Datasheet

© 2007 Microchip Technology Inc. DS39599G-page 205
PIC18F2220/2320/4220/4320
To set up an Asynchronous Transmission:
1. Initialize the SPBRG register for the appropriate
baud rate. If a high-speed baud rate is desired,
set bit BRGH (Section 18.2 “USART Baud
Rate Generator (BRG)”).
2. Enable the asynchronous serial port by clearing
bit, SYNC, and setting bit, SPEN.
3. If interrupts are desired, set enable bit, TXIE.
4. If 9-bit transmission is desired, set Transmit bit,
TX9. Can be used as address/data bit.
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 the GIE and PEIE
bits in the INTCON register (INTCON<7:6>) are
set.
FIGURE 18-5: ASYNCHRONOUS RECEPTION
TABLE 18-7: REGISTERS ASSOCIATED WITH ASYNCHRONOUS RECEPTION
Start
bit
bit 7/8bit 1bit 0 bit 7/8
bit 0Stop
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) bit to be set.
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
INTCON GIE/GIEH PEIE/
GIEL
TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF 0000 000x 0000 000u
PIR1
PSPIF
(1)
ADIF RCIF TXIF SSPIF CCP1IF TMR2IF TMR1IF 0000 0000 0000 0000
PIE1 PSPIE
(1)
ADIE RCIE TXIE SSPIE CCP1IE TMR2IE TMR1IE 0000 0000 0000 0000
IPR1 PSPIP
(1)
ADIP RCIP TXIP SSPIP CCP1IP TMR2IP TMR1IP 1111 1111 1111 1111
RCSTA SPEN RX9 SREN CREN ADDEN FERR OERR RX9D 0000 000x 0000 000x
RCREG USART Receive Register 0000 0000 0000 0000
TXSTA
CSRC TX9 TXEN SYNC —BRGHTRMT TX9D 0000 -010 0000 -010
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: The PSPIF, PSPIE and PSPIP bits are reserved on the PIC18F2X20 devices; always maintain these bits clear.