PIC16F193X Datasheet, PDF (283/418 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology

22.3 SPI Mode
The SPI mode allows 8 bits of data to be synchronously
transmitted and received simultaneously. All four clock
modes of SPI are supported in both Master and Slave
modes. To accomplish communication, 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)
Figure 22-1 shows the block diagram of the MSSP
module when operating in SPI mode.
22.3.1 REGISTERS
The MSSP module has five registers for SPI mode
operation. These are:
• MSSP STATUS register (SSPSTAT)
• MSSP Control Register 1 (SSPCON1)
• MSSP Control Register 3 (SSPCON3)
• MSSP Data Buffer register (SSPBUF)
• MSSP Address register (SSPADD)
• MSSP Shift register (SSPSR)
(Not directly accessible)
SSPCON1 and SSPSTAT are the control and STATUS
registers in SPI mode operation. The SSPCON1 regis-
ter is readable and writable. The lower 6 bits of the
SSPSTAT are read-only. The upper two bits of the
SSPSTAT are read/write.
In one SPI master mode, SSPADD can be loaded with
a value used in the Baud Rate Generator. More infor-
mation on the Baud Rate Generator is available in
Section 22.7 “Baud Rate Generator”.
SSPSR is the shift register used for shifting data in and
out. SSPBUF provides indirect access to the SSPSR
register. SSPBUF is the buffer register to which data
bytes are written, and from which data bytes are read.
In receive operations, SSPSR and SSPBUF together
create a buffered receiver. When SSPSR receives a
complete byte, it is transferred to SSPBUF and the
SSPIF interrupt is set.
During transmission, the SSPBUF is not buffered. A
write to SSPBUF will write to both SSPBUF and
SSPSR.
PIC16F193X/LF193X
22.3.2 OPERATIONS
When initializing the SPI, several options need to be
specified. This is done by programming the appropriate
control bits (SSPCON1<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)
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
SSPSTAT register, and the interrupt flag bit, SSPIF, 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 SSPCON1 register, will be set. User software
must clear the WCOL bit to allow the following write(s)
to the SSPBUF register to complete successfully.
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. 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.
The SSPSR is not directly readable or writable and can
only be accessed by addressing the SSPBUF register.
Additionally, the SSPSTAT register indicates the
various Status conditions.
© 2008 Microchip Technology Inc.
Preliminary
DS41364A-page 281