PIC18F14K50-I/SO【PDF 51/285 页】IC PIC MCU FLASH 8KX16 20-SOIC

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Sheet目录3871

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PIC18F/LF1XK50

DS41350E-page 144

Preliminary

2010 Microchip Technology Inc.

15.2.5

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 15-2) 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.

This

then,

would

give

waveforms

for

SPI

communication as shown in Figure 15-3, Figure 15-5

and Figure 15-6, where the MSB is transmitted first. In

Master mode, the SPI clock rate (bit rate) is user

programmable to be one of the following:

FOSC/4 (or TCY)

FOSC/16 (or 4 TCY)

FOSC/64 (or 16 TCY)

Timer2 output/2

This allows a maximum data rate (at 64 MHz) of

16.00 Mbps.

Figure 15-3 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 15-3:

SPI MODE WAVEFORM (MASTER MODE)

SCK

(CKP = 0

SCK

(CKP = 1

SCK

(CKP = 0

SCK

(CKP = 1

4 Clock

Modes

Input

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)

bit 0

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