PIC16F1933_11 Datasheet, PDF (227/430 Pages) Microchip Technology – 28-Pin Flash-Based, 8-Bit CMOS Microcontrollers LCD Driver and nanoWatt XLP Technology

PIC16(L)F1933
24.2.3 SPI MASTER MODE
The master can initiate the data transfer at any time
because it controls the SCK line. The master
determines when the slave (Processor 2, Figure 24-5)
is to broadcast data by the software protocol.
In Master mode, the data is transmitted/received as
soon as the SSPBUF register is written to. If the SPI is
only going to receive, the SDO output could be dis-
abled (programmed as an input). The SSPSR register
will continue to shift in the signal present on the SDI pin
at the programmed clock rate. As each byte is
received, it will be loaded into the SSPBUF register as
if a normal received byte (interrupts and Status bits
appropriately set).
The clock polarity is selected by appropriately
programming the CKP bit of the SSPCON1 register
and the CKE bit of the SSPSTAT register. This then,
would give waveforms for SPI communication as
shown in Figure 24-6, Figure 24-8 and Figure 24-9,
where the MSB is transmitted first. In Master mode, the
SPI clock rate (bit rate) is user programmable to be one
of the following:
• FOSC/4 (or TCY)
• FOSC/16 (or 4 * TCY)
• FOSC/64 (or 16 * TCY)
• Timer2 output/2
• Fosc/(4 * (SSPADD + 1))
Figure 24-6 shows the waveforms for Master mode.
When the CKE bit is set, the SDO data is valid before
there is a clock edge on SCK. The change of the input
sample is shown based on the state of the SMP bit. The
time when the SSPBUF is loaded with the received
data is shown.
FIGURE 24-6:
Write to
SSPBUF
SCK
(CKP = 0
CKE = 0)
SCK
(CKP = 1
CKE = 0)
SCK
(CKP = 0
CKE = 1)
SCK
(CKP = 1
CKE = 1)
SDO
(CKE = 0)
SDO
(CKE = 1)
SDI
(SMP = 0)
Input
Sample
(SMP = 0)
SDI
(SMP = 1)
Input
Sample
(SMP = 1)
SSPIF
SSPSR to
SSPBUF
SPI MODE WAVEFORM (MASTER MODE)
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
bit 7
bit 0
bit 7
bit 0
4 Clock
Modes
 2011 Microchip Technology Inc.
Preliminary
DS41575A-page 227