Datasheet

 2003-2013 Microchip Technology Inc. DS30491D-page 247
PIC18F6585/8585/6680/8680
18.4 USART Synchronous Slave Mode
Synchronous Slave mode is entered by clearing bit
CSRC (TXSTA<7>). This mode differs from the
Synchronous Master mode in that the shift clock is sup-
plied externally at the RC6/TX/CK pin (instead of being
supplied internally in Master mode). This allows the
device to transfer or receive data while in any low-power
mode.
18.4.1 USART 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 TXREG 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 TXREG register.
c) Flag bit TXIF will not be set.
d) When the first word has been shifted out of TSR,
the TXREG register will transfer the second word
to the TSR and flag bit TXIF will now be set.
e) If enable bit TXIE 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 TXIE.
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 TXREG
register.
8. If using interrupts, ensure that the GIE and PEIE
bits in the INTCON register (INTCON<7:6>) are
set.
TABLE 18-9: REGISTERS ASSOCIATED WITH SYNCHRONOUS SLAVE TRANSMISSION
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
ADIF RCIF TXIF SSPIF CCP1IF TMR2IF TMR1IF 0000 0000 0000 0000
PIE1 PSPIE
ADIE RCIE TXIE SSPIE CCP1IE TMR2IE TMR1IE 0000 0000 0000 0000
IPR1 PSPIP
ADIP RCIP TXIP SSPIP CCP1IP TMR2IP TMR1IP 1111 1111 1111 1111
RCSTA SPEN RX9 SREN CREN
ADDEN FERR OERR RX9D 0000 000x 0000 000x
TXREG USART Transmit Register 0000 0000 0000 0000
TXSTA CSRC TX9 TXEN SYNC
SENDB BRGH TRMT TX9D 0000 0010 0000 0010
BAUDCON
— RCIDL — SCKP BRG16 — WUE ABDEN -1-1 0-00 -1-1 0-00
SPBRGH Baud Rate Generator Register, High Byte 0000 0000 0000 0000
SPBRG Baud Rate Generator Register, Low Byte 0000 0000 0000 0000
Legend: x = unknown, - = unimplemented, read as ‘0’. Shaded cells are not used for synchronous slave transmission.
18F8680.book Page 247 Tuesday, January 29, 2013 1:32 PM