PIC16F870/871
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 9.1)
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 9-2: 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 9-3: ASYNCHRONOUS MASTER TRANSMISSION (BACK TO BACK)
Write to TXREG
Word 2
Word 1
BRG output
(shift clock)
RC6/TX/CK (pin)
TXIF bit
(interrupt reg. flag)
Start Bit
Start Bit
Word 2
Bit 0
Bit 1
Word 1
Bit 7/8
Bit 0
Stop Bit
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 9-5:
REGISTERS ASSOCIATED WITH ASYNCHRONOUS TRANSMISSION
Value on:
POR,
BOR
Value on
all other
Resets
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(1)
—
—
0Ch
18h
19h
8Ch
98h
99h
PIR1
PSPIF
ADIF
RCIF
TXIF
CCP1IF TMR2IF TMR1IF 0000 -000 0000 -000
RCSTA
SPEN
RX9
SREN CREN
FERR
OERR
RX9D 0000 -00x 0000 -00x
TXREG USART Transmit Register
0000 0000 0000 0000
(1)
PIE1
PSPIE
CSRC
ADIE
TX9
RCIE
TXIE
—
—
CCP1IE TMR2IE TMR1IE 0000 -000 0000 -000
TXSTA
TXEN
SYNC
BRGH
TRMT
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 transmission.
Note 1: Bits PSPIE and PSPIF are reserved on the PIC16F870; always maintain these bits clear.
DS30569A-page 68
Preliminary
1999 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
