PIC16F877-20L Datasheet, PDF (108/218 Pages) Microchip Technology – 28/40-Pin 8-Bit CMOS FLASH Microcontrollers

PIC16F87X
FIGURE 10-11: SYNCHRONOUS RECEPTION (MASTER MODE, SREN)
Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
RC7/RX/DT pin
bit0
bit1
bit2
bit3
bit4
bit5
bit6
bit7
RC6/TX/CK pin
Write to
bit SREN
SREN bit
CREN bit ^'0'
'0'
RCIF bit
(Interrupt)
Read
RXREG
Note: Timing diagram demonstrates SYNC Master mode with bit SREN = '1' and bit BRG = '0'.
10.4 USART Synchronous Slave Mode
Synchronous Slave mode differs from the Master mode
in the fact that the shift clock is supplied 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 SLEEP mode. Slave mode is
entered by clearing bit CSRC (TXSTA<7>).
10.4.1 USART SYNCHRONOUS SLAVE
TRANSMIT
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 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 and if the global interrupt
is enabled, the program will branch to the inter-
rupt vector (0004h).
When setting up a Synchronous Slave Transmission,
follow these steps:
1. Enable the synchronous slave serial port by set-
ting bits SYNC and SPEN and clearing bit
CSRC.
2. Clear bits CREN and SREN.
3. If interrupts are desired, then set enable bit
TXIE.
4. If 9-bit transmission is desired, then 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 GIE and PEIE
(bits 7 and 6) of the INTCON register are set.
TABLE 10-10: REGISTERS ASSOCIATED WITH SYNCHRONOUS SLAVE TRANSMISSION
Address 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
0Bh, 8Bh, INTCON
10Bh,18Bh
0Ch
PIR1
GIE
PSPIF⁽¹⁾
PEIE
ADIF
T0IE
RCIF
INTE
TXIF
RBIE T0IF INTF R0IF 0000 000x 0000 000u
SSPIF CCP1IF TMR2IF TMR1IF 0000 0000 0000 0000
18h
RCSTA SPEN RX9 SREN CREN ADDEN FERR OERR RX9D 0000 000x 0000 000x
19h
TXREG USART Transmit Register
0000 0000 0000 0000
8Ch
PIE1
PSPIE⁽¹⁾ ADIE RCIE TXIE SSPIE CCP1IE TMR2IE TMR1IE 0000 0000 0000 0000
98h
TXSTA CSRC TX9 TXEN SYNC — BRGH TRMT TX9D 0000 -010 0000 -010
99h
SPBRG Baud Rate Generator Register
0000 0000 0000 0000
Legend: x = unknown, - = unimplemented, read as '0'. Shaded cells are not used for synchronous slave transmission.
Note 1: Bits PSPIE and PSPIF are reserved on PIC16F873/876 devices; always maintain these bits clear.
DS30292D-page 108
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