When the application software is expecting to receive valid data from Extract PIC16LF870 MCU Code, the SSPBUF should be read before the next byte of data to transfer is written to the SSPBUF. Buffer Full bit, BF (SSPSTAT<0>), 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 SSP interrupt is used to determine when the transmission/reception has completed. The SSPBUF must be read and/or written if code being extracted from MCU.
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 14-1 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 SSP Status register (SSPSTAT) indicates the various status conditions.
To enable the serial port, SSP Enable bit, SSPEN (SSPCON<5>), 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 after MCU code being extracted.
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<4> bit cleared
- SCK (Master mode) must have TRISC<6> bit cleared
- SCK (Slave mode) must have TRISC<6> 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.
