Datasheet

PIC18F45J10 FAMILY
DS39682E-page 212 © 2009 Microchip Technology Inc.
17.4 EUSART 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 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.
17.4.1 EUSART SYNCHRONOUS
SLAVE TRANSMISSION
The operation of the Synchronous Master and Slave
modes is 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 the 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 17-9: 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 47
PIR1 PSPIF
(1)
ADIF RCIF TXIF SSP1IF CCP1IF TMR2IF TMR1IF 49
PIE1
PSPIE
(1)
ADIE RCIE TXIE SSP1IE CCP1IE TMR2IE TMR1IE 49
IPR1 PSPIP
(1)
ADIP RCIP TXIP SSP1IP CCP1IP TMR2IP TMR1IP 49
RCSTA SPEN RX9 SREN CREN
ADDEN FERR OERR RX9D 49
TXREG EUSART Transmit Register 49
TXSTA CSRC TX9 TXEN SYNC
SENDB BRGH TRMT TX9D 49
BAUDCON
ABDOVF RCIDL — SCKP BRG16 — WUE ABDEN 49
SPBRGH EUSART Baud Rate Generator Register High Byte 49
SPBRG EUSART Baud Rate Generator Register Low Byte 49
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used for synchronous slave transmission.
Note 1: These bits are not implemented on 28-pin devices and should be read as ‘0’.