PIC16F62X
Steps to follow when setting up an Asynchronous
Transmission:
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.
1. Initialize the SPBRG register for the appropriate
baud rate. If a high speed baud rate is desired,
set bit BRGH. (Section 12.1)
6. If 9-bit transmission is selected, the ninth bit
should be loaded in bit TX9D.
2. Enable the asynchronous serial port by clearing
bit SYNC and setting bit SPEN.
7. Load data to the TXREG register (starts trans-
mission).
3. If interrupts are desired, then set enable bit
TXIE.
FIGURE 12-6: ASYNCHRONOUS MASTER TRANSMISSION
Write to TXREG
Word 1
BRG output
(shift clock)
RB2/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 12-7: ASYNCHRONOUS MASTER TRANSMISSION (BACK TO BACK)
Write to TXREG
Word 2
Word 1
BRG output
(shift clock)
RB2/TX/CK (pin)
Start Bit
Start Bit
WORD 2
Bit 0
Bit 1
Bit 7/8
Bit 0
Stop Bit
TXIF bit
(interrupt reg. flag)
WORD 1
TRMT bit
(Transmit shift
reg. empty flag)
WORD 1
Transmit Shift Reg.
WORD 2
Transmit Shift Reg.
Note: This timing diagram shows two consecutive transmissions.
TABLE 12-6: REGISTERS ASSOCIATED WITH ASYNCHRONOUS TRANSMISSION
Value on
all other
Resets
Value on
POR
Address Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0000 -000 0000 -000
0000 -00x 0000 -00x
0000 0000 0000 0000
0000 -000 0000 -000
0000 -010 0000 -010
0000 0000 0000 0000
0Ch
18h
19h
8Ch
PIR1
EEIF
CMIF
RCIF
TXIF
—
CCP1IF TMR2IF TMR1IF
FERR OERR RX9D
RCSTA
SPEN
RX9
SREN CREN ADEN
TXREG USART Transmit Register
PIE1
EEIE
CMIE
TX9
RCIE
TXIE
—
—
CCP1IE TMR2IE TMR1IE
BRGH TRMT TX9D
98h
99h
TXSTA
CSRC
TXEN
SYNC
SPBRG Baud Rate Generator Register
Legend: x= unknown, -= unimplemented locations read as '0'. Shaded cells are not used for Asynchronous Transmission.
1999 Microchip Technology Inc.
Preliminary
DS40300B-page 79
MICROCHIP [ MICROCHIP ]
