PIC18FXX39 Datasheet, PDF (129/322 Pages) Microchip Technology – Enhanced FLASH Microcontrollers with Single Phase Induction Motor Control Kernel

PIC18FXX39
16.3.3 ENABLING SPI I/O
To enable the serial port, SSP Enable bit, SSPEN
(SSPCON1<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. 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
cleared
• 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
overridden by programming the corresponding data
direction (TRIS) register to the opposite value.
16.3.4 TYPICAL CONNECTION
Figure 16-2 shows a typical connection between two
microcontrollers. The master controller (Processor 1)
initiates the data transfer by sending the SCK signal.
Data is shifted out of both shift registers on their pro-
grammed clock edge, and latched on the opposite
edge of the clock. Both processors should be pro-
grammed to the same Clock Polarity (CKP), then both
controllers would send and receive data at the same
time. Whether the data is meaningful (or dummy data)
depends on the application software. This leads to
three scenarios for data transmission:
• Master sends data—Slave sends dummy data
• Master sends data—Slave sends data
• Master sends dummy data—Slave sends data
FIGURE 16-2:
SPI MASTER/SLAVE CONNECTION
SPI Master SSPM3:SSPM0 = 00xxb
SDO
Serial Input Buffer
(SSPBUF)
SPI Slave SSPM3:SSPM0 = 010xb
SDI
Serial Input Buffer
(SSPBUF)
Shift Register
(SSPSR)
MSb
LSb
PROCESSOR 1
SDI
Serial Clock
SCK
SDO
Shift Register
(SSPSR)
MSb
LSb
SCK
PROCESSOR 2
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Preliminary
DS30485B-page 129