Datasheet

Table Of Contents
2010 Microchip Technology Inc. Preliminary DS39979A-page 271
PIC18F87J72 FAMILY
20.5 AUSART Synchronous Slave Mode
Synchronous Slave mode is entered by clearing bit,
CSRC (TXSTA2<7>). This mode differs from the
Synchronous Master mode in that the shift clock is
supplied externally at the CK2 pin (instead of being
supplied internally in Master mode). This allows the
device to transfer or receive data while in any
low-power mode.
20.5.1 AUSART SYNCHRONOUS
SLAVE TRANSMIT
The operation of the Synchronous Master and Slave
modes are identical except in the case of the Sleep
mode.
If two words are written to the TXREG2 and then the
SLEEP instruction is executed, the following will occur:
a) The first word will immediately transfer to the
TSR register and transmit.
b) The second word will remain in the TXREG2
register.
c) Flag bit, TX2IF, will not be set.
d) When the first word has been shifted out of TSR,
the TXREG2 register will transfer the second
word to the TSR and flag bit, TX2IF, will now be
set.
e) If enable bit, TX2IE, is set, the interrupt will wake
the chip from Sleep. If the global interrupt is
enabled, the program will branch to the interrupt
vector.
To set up a Synchronous Slave Transmission:
1. Enable the synchronous slave serial port by
setting bits, SYNC and SPEN, and clearing bit,
CSRC.
2. Clear bits, CREN and SREN.
3. If interrupts are desired, set enable bit, TX2IE.
4. If 9-bit transmission is desired, set bit, TX9.
5. Enable the transmission by setting enable bit,
TXEN.
6. If 9-bit transmission is selected, the ninth bit
should be loaded in bit, TX9D.
7. Start transmission by loading data to the
TXREG2 register.
8. If using interrupts, ensure that the GIE and PEIE
bits in the INTCON register (INTCON<7:6>) are
set.
TABLE 20-8: REGISTERS ASSOCIATED WITH SYNCHRONOUS SLAVE TRANSMISSION
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Reset
Values
on Page
INTCON GIE/GIEH PEIE/GIEL
TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF 49
PIR3 LCDIF RC2IF TX2IF CTMUIF CCP2IF CCP1IF RTCCIF 52
PIE3 LCDIE RC2IE TX2IE CTMUIE CCP2IE CCP1IE RTCCIE 52
IPR3
LCDIP RC2IP TX2IP CTMUIP CCP2IP CCP1IP RTCCIP 52
RCSTA2 SPEN RX9 SREN CREN ADDEN FERR OERR RX9D 54
TXREG2 AUSART Transmit Register 54
TXSTA2 CSRC TX9 TXEN SYNC
BRGH TRMT TX9D 54
SPBRG2 AUSART Baud Rate Generator Register 54
LATG U2OD U1OD LATG4 LATG3 LATG2 LATG1 LATG0 52
Legend: — = unimplemented, read as0. Shaded cells are not used for synchronous slave transmission.