PIC18C658 MICROCHIP [Microchip Technology], PIC18C658 Datasheet - Page 142

• Manufacturer Part Number: PIC18C658
• Description: High-Performance Microcontrollers with CAN Module
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18CXX8
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 (BF) bit (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 15-1 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 reg-
ister. Additionally, the MSSP status register (SSPSTAT
register) indicates the various status conditions.
EXAMPLE 15-1: LOADING THE SSPBUF (SSPSR) REGISTER
DS30475A-page 142
LOOP BTFSS SSPSTAT, BF
GOTO
MOVF
MOVWF RXDATA
MOVF
MOVWF SSPBUF
LOOP
SSPBUF, W
TXDATA, W
;Has data been received (transmit complete)?
;No
;WREG reg = contents of SSPBUF
;Save in user RAM, if data is meaningful
;W reg = contents of TXDATA
;New data to xmit
Advanced Information
15.3.2
To enable the serial port, SSP Enable bit, SSPEN
(SSPCON1 register), must be set. To reset or reconfig-
ure 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 func-
tion, 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
• SCK (Slave mode) must have TRISC<3> bit set
• SS must have TRISC<4> bit set
Any serial port function that is not desired may be over-
ridden by programming the corresponding data direc-
tion (TRIS) register to the opposite value.
cleared
ENABLING SPI I/O
 2000 Microchip Technology Inc.