PIC18F47J53 Datasheet, PDF (297/586 Pages) Microchip Technology – 28/44-Pin, High-Performance USB Microcontrollers with nanoWatt XLP Technology

PIC18F47J53 FAMILY
20.3.6 MASTER MODE
The master can initiate the data transfer at any time
because it controls the SCKx. The master determines
when the slave (Processor 2, Figure 20-2) is to
broadcast data by the software protocol.
In Master mode, the data is transmitted/received as
soon as the SSPxBUF register is written to. If the SPI
is only going to receive, the SDOx output could be dis-
abled (programmed as an input). The SSPxSR register
will continue to shift in the signal present on the SDIx
pin at the programmed clock rate. As each byte is
received, it will be loaded into the SSPxBUF register as
if it is a normal received byte (interrupts and status bits
are appropriately set). This could be useful in receiver
applications as a “Line Activity Monitor” mode.
The CKP is selected by appropriately programming the
CKP bit (SSPxCON1<4>). This then, would give
waveforms for SPI communication, as illustrated in
Figure 20-3, Figure 20-5 and Figure 20-6, where the
Most Significant Byte (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/8 (or 2 • TCY)
• FOSC/16 (or 4 • TCY)
• FOSC/64 (or 16 • TCY)
• Timer2 output/2
When using the Timer2 output/2 option, the Period
Register 2 (PR2) can be used to determine the SPI bit
rate. However, only PR2 values of 0x01 to 0xFF are
valid in this mode.
Figure 20-3 illustrates the waveforms for Master mode.
When the CKE bit is set, the SDOx data is valid before
there is a clock edge on SCKx. The change of the input
sample is shown based on the state of the SMP bit. The
time when the SSPxBUF is loaded with the received
data is shown.
FIGURE 20-3:
Write to
SSPxBUF
SCKx
(CKP = 0
CKE = 0)
SCKx
(CKP = 1
CKE = 0)
SCKx
(CKP = 0
CKE = 1)
SCKx
(CKP = 1
CKE = 1)
SDOx
(CKE = 0)
SDOx
(CKE = 1)
SDIx
(SMP = 0)
Input
Sample
(SMP = 0)
SDIx
(SMP = 1)
Input
Sample
(SMP = 1)
SSPxIF
SSPxSR to
SSPxBUF
SPI MODE WAVEFORM (MASTER MODE)
4 Clock
Modes
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
Next Q4 Cycle
after Q2
 2010 Microchip Technology Inc.
Preliminary
DS39964B-page 297