
2004 Microchip Technology Inc.
Preliminary
DS39637A-page 245
PIC18F2480/2580/4480/4580
18.4
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.
18.4.1
EUSART 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 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
TXREGx 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
Reset
Values
on page
INTCON
PIR1
PIE1
IPR1
RCSTA
TXREG
TXSTA
BAUDCON
SPBRGH
SPBRG
Legend:
Note 1:
GIE/GIEH PEIE/GIEL
PSPIF
(1)
PSPIE
(1)
PSPIP
(1)
SPEN
EUSART Transmit Register
CSRC
ABDOVF
EUSART
Baud Rate Generator Register High Byte
EUSART Baud Rate Generator Register Low Byte
— = unimplemented, read as ‘
0
’. Shaded cells are not used for synchronous slave transmission.
Reserved in PIC18F2X80 devices; always maintain these bits clear.
TMR0IE
RCIF
RCIE
RCIP
SREN
INT0IE
TXIF
TXIE
TXIP
CREN
RBIE
SSPIF
SSPIE
SSPIP
ADDEN
TMR0IF
CCP1IF
CCP1IE
CCP1IP
FERR
INT0IF
TMR2IF
TMR2IE
TMR2IP
OERR
RBIF
TMR1IF
TMR1IE
TMR1IP
RX9D
49
52
52
52
51
51
51
51
51
51
ADIF
ADIE
ADIP
RX9
TX9
RCIDL
TXEN
—
SYNC
SCKP
SENDB
BRG16
BRGH
—
TRMT
WUE
TX9D
ABDEN