Datasheet
2011 Microchip Technology Inc. DS39931D-page 345
PIC18F46J50 FAMILY
20.4 EUSART Synchronous Slave
Mode
Synchronous Slave mode is entered by clearing bit,
CSRC (TXSTAx<7>). This mode differs from the
Synchronous Master mode in that the shift clock is sup-
plied externally at the CKx pin (instead of being supplied
internally in Master mode). This allows the device to
transfer or receive data while in any low-power mode.
20.4.1 EUSART SYNCHRONOUS SLAVE
TRANSMISSION
The operation of the Synchronous Master and Slave
modes is identical, except in the case of Sleep mode.
If two words are written to the TXREGx 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 TXREGx
register.
c) Flag bit, TXxIF, will not be set.
d) When the first word has been shifted out of TSR,
the TXREGx register will transfer the second word
to the TSR and flag bit, TXxIF, will now be set.
e) If enable bit, TXxIE, 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, TXxIE.
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
TXREGx register.
8. If using interrupts, ensure that the GIE and PEIE
bits in the INTCON register (INTCON<7:6>) are
set.
TABLE 20-9: 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 69
PIR1 PMPIF
(1)
ADIF RC1IF TX1IF SSP1IF CCP1IF TMR2IF TMR1IF 72
PIE1 PMPIE
(1)
ADIE RC1IE TX1IE SSP1IE CCP1IE TMR2IE TMR1IE 72
IPR1
PMPIP
(1)
ADIP RC1IP TX1IP SSP1IP CCP1IP TMR2IP TMR1IP 72
PIR3 SSP2IF BCL2IF RC2IF TX2IF TMR4IF CTMUIF TMR3GIF RTCCIF 72
PIE3 SSP2IE BCL2IE RC2IE TX2IE TMR4IE CTMUIE TMR3GIE RTCCIE 72
IPR3
SSP2IP BCL2IP RC2IP TX2IP TMR4IP CTMUIP TMR3GIP RTCCIP 72
RCSTAx SPEN RX9 SREN CREN ADDEN FERR OERR RX9D 72
TXREGx EUSARTx Transmit Register 72
TXSTAx CSRC TX9 TXEN SYNC
SENDB BRGH TRMT TX9D 72
BAUDCONx ABDOVF RCIDL RXDTP TXCKP BRG16 — WUE ABDEN 73
SPBRGHx EUSARTx Baud Rate Generator Register High Byte 72
SPBRGx EUSARTx Baud Rate Generator Register Low Byte 72
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used for synchronous slave transmission.
Note 1: These pins are only available on 44-pin devices.