PIC16F882_09 Datasheet, PDF (185/328 Pages) Microchip Technology – 28/40/44-Pin, Enhanced Flash-Based 8-Bit CMOS Microcontrollers with nanoWatt Technology

PIC16F882/883/884/886/887
13.3 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 communication,
typically three pins are used:
• Serial Data Out (SDO) – RC5/SDO
• Serial Data In (SDI) – RC4/SDI/SDA
• Serial Clock (SCK) – RC3/SCK/SCL
Additionally, a fourth pin may be used when in any
Slave mode of operation:
• Slave Select (SS) – RA5/SS/AN4
13.3.1 OPERATION
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 13-1 shows the block diagram of the MSSP
module, when in SPI mode.
FIGURE 13-1:
MSSP BLOCK DIAGRAM
(SPI MODE)
Internal
Data Bus
Read
Write
SSPBUF Reg
SDI
SDO
SSPSR Reg
bit 0
Shift
Clock
SS Control
Enable
SS
Edge
Select
2
Clock Select
SCK
SSPM<3:0>
SMP:CKE ₄
2
( ) TMR2 Output
2
Edge
Select
Prescaler TOSC
4, 16, 64
Data to TX/RX in SSPSR
TRIS bit
Note: I/O pins have diode protection to VDD and VSS.
The MSSP consists of a transmit/receive shift register
(SSPSR) and a buffer register (SSPBUF). The SSPSR
shifts the data in and out of the device, MSb first. The
SSPBUF holds the data that was written to the SSPSR,
until the received data is ready. Once the 8 bits of data
have been received, that byte is moved to the SSPBUF
register. Then, the buffer full-detect bit BF of the SSP-
STAT register and the interrupt flag bit SSPIF of the
PIR1 register are set. This double buffering of the
received data (SSPBUF) allows the next byte to start
reception before reading the data that was just
received. Any write to the SSPBUF register during
transmission/reception of data will be ignored, and the
write collision detect bit WCOL of the SSPCON register
will be set. User software must clear the WCOL bit so
that it can be determined if the following write(s) to the
SSPBUF register completed successfully.
© 2009 Microchip Technology Inc.
DS41291F-page 183