Datasheet

Table Of Contents
© 2009 Microchip Technology Inc. DS39689F-page 231
PIC18F2221/2321/4221/4321 FAMILY
19.4 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 power-managed
mode.
19.4.1 EUSART SYNCHRONOUS
SLAVE TRANSMISSION
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 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 the signal from the CK pin is to be inverted, set
the TXCKP bit.
5. If 9-bit transmission is desired, set bit, TX9.
6. Enable the transmission by setting enable bit,
TXEN.
7. If 9-bit transmission is selected, the ninth bit
should be loaded in bit TX9D.
8. Start transmission by loading data to the
TXREGx register.
9. If using interrupts, ensure that the GIE and PEIE
bits in the INTCON register (INTCON<7:6>) are
set.
TABLE 19-9: 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 55
PIR1
PSPIF
(1)
ADIF RCIF TXIF SSPIF CCP1IF TMR2IF TMR1IF 58
PIE1
PSPIE
(1)
ADIE RCIE TXIE SSPIE CCP1IE TMR2IE TMR1IE 58
IPR1
PSPIP
(1)
ADIP RCIP TXIP SSPIP CCP1IP TMR2IP TMR1IP 58
RCSTA SPEN RX9 SREN CREN ADDEN FERR OERR RX9D 57
TXREG EUSART Transmit Register 57
TXSTA CSRC TX9 TXEN SYNC
SENDB BRGH TRMT TX9D 57
BAUDCON ABDOVF RCIDL RXDTP TXCKP BRG16 WUE ABDEN 57
SPBRGH EUSART Baud Rate Generator Register High Byte 57
SPBRG EUSART Baud Rate Generator Register Low Byte 57
Legend: — = unimplemented, read as0’. Shaded cells are not used for synchronous slave transmission.
Note 1: These bits are unimplemented on 28-pin devices and read as ‘0’.