PIC16F872 Datasheet, PDF (57/160 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS FLASH Microcontroller

9.1 SPI Mode
The SPI mode allows 8 bits of data to be synchronously
transmitted and received simultaneously. All four
modes of SPI are supported. To accomplish communi-
cation, typically three pins are used:
• Serial Data Out (SDO)
• Serial Data In (SDI)
• Serial Clock (SCK)
Additionally, a fourth pin may be used when in a slave
mode of operation:
• Slave Select (SS)
When initializing the SPI, several options need to be
specified. This is done by programming the appropriate
control bits (SSPCON<5:0> and SSPSTAT<7:6>).
These control bits allow the following to be specified:
• Master Mode (SCK is the clock output)
• Slave Mode (SCK is the clock input)
• Clock Polarity (Idle state of SCK)
• Data input sample phase
(middle or end of data output time)
• Clock edge
(output data on rising/falling edge of SCK)
• Clock Rate (Master mode only)
• Slave Select Mode (Slave mode only)
Figure 9-4 shows the block diagram of the MSSP mod-
ule when in SPI mode.
PIC16F872
FIGURE 9-1: MSSP BLOCK DIAGRAM
(SPI MODE)
Internal
Data Bus
Read
Write
SSPBUF reg
SDI
SDO
SSPSR reg
bit0
Shift
Clock
SS
SCK
SS Control
Enable
Edge
Select
2
Clock Select
SSPM3:SSPM0
SMP:CKE ₄
2
TMR2 output
2
Edge
Select
Prescaler TOSC
4, 16, 64
Data to TX/RX in SSPSR
Data direction bit
To enable the serial port, MSSP Enable bit, SSPEN
(SSPCON<5>) must be set. To reset or reconfigure SPI
mode, clear bit SSPEN, re-initialize the SSPCON reg-
isters, and then set bit SSPEN. 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> cleared
• SCK (Master mode) must have TRISC<3>
cleared
• SCK (Slave mode) must have TRISC<3> set
• SS must have TRISA<5> 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.
© 1999 Microchip Technology Inc.
Preliminary
DS30221A-page 57