PIC16F882-I datasheet(186/328 Pages) MICROCHIP

186 / 328 page

PIC16F882/883/884/886/887

DS41291F-page 184

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

(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

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