Datasheet
PIC16F882/883/884/886/887
DS41291G-page 188 2006-2012 Microchip Technology Inc.
When the application software is expecting to receive
valid data, the SSPBUF should be read before the next
byte of data to transfer is written to the SSPBUF. The
buffer full bit BF of the SSPSTAT register indicates
when SSPBUF has been loaded with the received data
(transmission is complete). When the SSPBUF is read,
the BF bit is cleared. This data may be irrelevant if the
SPI is only a transmitter. Generally, the MSSP Interrupt
is used to determine when the transmission/reception
has completed. The SSPBUF must be read and/or
written. If the interrupt method is not going to be used,
then software polling can be done to ensure that a write
collision does not occur. Example 13-1 shows the
loading of the SSPBUF (SSPSR) for data transmission.
The SSPSR is not directly readable or writable, and
can only be accessed by addressing the SSPBUF
register. Additionally, the MSSP STATUS register
(SSPSTAT register) indicates the various status
conditions.
13.3.2 ENABLING SPI I/O
To enable the serial port, SSP Enable bit SSPEN of the
SSPCON register must be set. To reset or reconfigure
SPI mode, clear the SSPEN bit, re-initialize the
SSPCON registers, and then set the SSPEN bit. This
configures the SDI, SDO, SCK and SS
pins as serial
port pins. For the pins to behave as the serial port
function, some must have their data direction bits (in
the TRIS register) appropriately programmed. That is:
• SDI is automatically controlled by the SPI module
• SDO must have TRISC<5> bit cleared
• SCK (Master mode) must have TRISC<3> bit
cleared
• SCK (Slave mode) must have TRISC<3> bit set
•SS
must have TRISA<5> bit set
Any serial port function that is not desired may be
overridden by programming the corresponding data
direction (TRIS) register to the opposite value.
EXAMPLE 13-1: LOADING THE SSPBUF (SSPSR) REGISTER
LOOP BTFSS SSPSTAT, BF ;Has data been received (transmit complete)?
GOTO LOOP ;No
MOVF SSPBUF, W ;WREG reg = contents of SSPBUF
MOVWF RXDATA ;Save in user RAM, if data is meaningful
MOVF TXDATA, W ;W reg = contents of TXDATA
MOVWF SSPBUF ;New data to xmit