PIC16F946 Datasheet, PDF (148/274 Pages) Microchip Technology – 64-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology

PIC16F946
11.3.2
USART SYNCHRONOUS MASTER
RECEPTION
Once Synchronous mode is selected, reception is
enabled by setting either enable bit, SREN
(RCSTA<5>), or enable bit, CREN (RCSTA<4>). Data
is sampled on the RC7/RX/DT/SDI/SDA/SEG8 pin on
the falling edge of the clock. If enable bit SREN is set,
then only a single word is received. If enable bit CREN
is set, the reception is continuous until CREN is
cleared. If both bits are set, CREN takes precedence.
After clocking the last bit, the received data in the
Receive Shift Register (RSR) is transferred to the
RCREG register (if it is empty). When the transfer is
complete, interrupt flag bit, RCIF (PIR1<5>), is set. The
actual interrupt can be enabled/disabled by set-
ting/clearing enable bit, RCIE (PIE1<5>). Flag bit RCIF
is a read-only bit which is reset by the hardware. In this
case, it is reset when the RCREG register has been
read and is empty. The RCREG is a double-buffered
register (i.e., it is a two-deep FIFO). It is possible for two
bytes of data to be received and transferred to the
RCREG FIFO and a third byte to begin shifting into the
RSR register. On the clocking of the last bit of the third
byte, if the RCREG register is still full, then Overrun
Error bit, OERR (RCSTA<1>), is set. The word in the
RSR will be lost. The RCREG register can be read
twice to retrieve the two bytes in the FIFO. Bit OERR
has to be cleared in software (by clearing bit CREN). If
bit OERR is set, transfers from the RSR to the RCREG
are inhibited so it is essential to clear bit OERR if it is
set. The ninth receive bit is buffered the same way as
the receive data. Reading the RCREG register will load
bit RX9D with a new value, therefore, it is essential for
the user to read the RCSTA register before reading
RCREG in order not to lose the old RX9D information.
When setting up a Synchronous Master Reception:
1. Initialize the SPBRG register for the appropriate
baud rate (Section 11.1 “USART Baud Rate
Generator (BRG)”).
2. Enable the synchronous master serial port by
setting bits SYNC, SPEN and CSRC.
3. Ensure bits CREN and SREN are clear.
4. If interrupts are desired, then set enable bit
RCIE.
5. If 9-bit reception is desired, then set bit RX9.
6. If a single reception is required, set bit SREN.
For continuous reception, set bit CREN.
7. Interrupt flag bit RCIF will be set when reception
is complete and an interrupt will be generated if
enable bit RCIE was set.
8. Read the RCSTA register to get the ninth bit (if
enabled) and determine if any error occurred
during reception.
9. Read the 8-bit received data by reading the
RCREG register.
10. If any error occurred, clear the error by clearing
bit CREN.
11. If using interrupts, ensure that GIE and PEIE
(bits 7 and 6) of the INTCON register are set.
TABLE 11-9: REGISTERS ASSOCIATED WITH SYNCHRONOUS MASTER RECEPTION
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 GIE
10Bh,18Bh
PEIE T0IE INTE RBIE T0IF
INTF
RBIF 0000 000x 0000 000x
0Ch
PIR1
EEIF ADIF RCIF TXIF SSPIF CCP1IF TMR2IF TMR1IF 0000 0000 0000 0000
18h
RCSTA SPEN RX9 SREN CREN ADDEN FERR OERR RX9D 0000 000x 0000 000x
1Ah
RCREG USART Receive Data Register
0000 0000 0000 0000
8Ch
PIE1
EEIE 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 master reception.
DS41265A-page 146
Preliminary
© 2005 Microchip Technology Inc.