Microchip Technology MA180025 Data Sheet
PIC18F87J90 FAMILY
DS39933D-page 216
2010 Microchip Technology Inc.
18.3.6
MASTER MODE
The master can initiate the data transfer at any time
because it controls the SCK. The master determines
when the slave (Processor 2, Figure 18-2) will
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 it was a normal received byte (interrupts and status
bits appropriately set). This could be useful in receiver
applications as a “Line Activity Monitor” mode.
because it controls the SCK. The master determines
when the slave (Processor 2, Figure 18-2) will
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 it was a normal received byte (interrupts and status
bits appropriately set). This could be useful in receiver
applications as a “Line Activity Monitor” mode.
The clock polarity is selected by appropriately
programming the CKP bit (SSPCON1<4>). This, then,
would give waveforms for SPI communication, as
shown in Figure 18-3, Figure 18-5 and Figure 18-6,
where the MSB is transmitted first. In Master mode, the
SPI clock rate (bit rate) is user-programmable to be one
of the following:
• F
programming the CKP bit (SSPCON1<4>). This, then,
would give waveforms for SPI communication, as
shown in Figure 18-3, Figure 18-5 and Figure 18-6,
where the MSB is transmitted first. In Master mode, the
SPI clock rate (bit rate) is user-programmable to be one
of the following:
• F
OSC
/4 (or T
CY
)
• F
OSC
/16 (or 4 • T
CY
)
• F
OSC
/64 (or 16 • T
CY
)
• Timer2 output/2
This allows a maximum data rate (at 40 MHz) of
10.00 Mbps.
Figure 18-3 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.
This allows a maximum data rate (at 40 MHz) of
10.00 Mbps.
Figure 18-3 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 18-3:
SPI MODE WAVEFORM (MASTER MODE)
SCK
(CKP = 0
SCK
(CKP = 1
SCK
(CKP = 0
SCK
(CKP = 1
4 Clock
Modes
Input
Sample
Sample
Input
Sample
SDI
bit 7
bit 0
SDO
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
bit 7
SDI
SSPIF
(SMP = 1)
(SMP = 0)
(SMP = 1)
CKE = 1)
CKE = 0)
CKE = 1)
CKE = 0)
(SMP = 0)
Write to
SSPBUF
SSPSR to
SSPBUF
SDO
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
(CKE = 0)
(CKE = 1)
Next Q4 Cycle
after Q2
after Q2
bit 0