参数资料
型号: KSZ8864RMNI
厂商: Micrel Inc
文件页数: 75/111页
文件大小: 0K
描述: IC ETHERNET SWITCH 4PORT 64QFN
特色产品: KSZ8864RMN Ethernet Switches
标准包装: 348
系列: *
其它名称: 576-3995
PIC16C9XX
DS30444E - page 66
1997 Microchip Technology Inc.
To enable the serial port, SSP Enable bit, SSPEN
(SSPCON<5>) must be set. To reset or recongure SPI
mode, clear bit SSPEN, re-initialize the SSPCON reg-
ister, and then set bit SSPEN. This congures the SDI,
SDO, SCK, and SS pins as serial port pins. For the pins
to behave as the serial port function, they must have
their data direction bits (in the TRISC register) appro-
priately programmed. That is:
SDI must have TRISC<4> set
SDO must have TRISC<5> cleared
SCK (Master mode) must have TRISC<3>
cleared
SCK (Slave mode) must have TRISC<3> set
SS must have TRISA<5> set
Any serial port function that is not desired may be over-
ridden by programming the corresponding data direc-
tion (TRIS) register to the opposite value. An example
would be in master mode where you are only sending
data (to a display driver), then both SDI and SS could
be used as general purpose outputs by clearing their
corresponding TRIS register bits.
Figure 11-4 shows a typical connection between two
microcontrollers. The master controller (Processor 1)
initiates the data transfer by sending the SCK signal.
Data is shifted out of both shift registers on their pro-
grammed clock edge, and latched on the opposite edge
of the clock. Both processors should be programmed to
same Clock Polarity (CKP), then both controllers would
send and receive data at the same time. Whether the
data is meaningful (or dummy data) depends on the
application software. This leads to three scenarios for
data transmission:
Master sends data — Slave sends dummy data
Master sends data — Slave sends data
Master sends dummy data — Slave sends data
The master can initiate the data transfer at any time
because it controls the SCK. The master determines
when the slave (Processor 2) is to broadcast data by
the rmware 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 SCK output could be disabled
(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). This could be useful in receiver applications as a
“line activity monitor” mode.
In slave mode, the data is transmitted and received as
the external clock pulses appear on SCK. When the last
bit is latched the interrupt ag bit SSPIF (PIR1<3>) is
set.
The clock polarity is selected by appropriately program-
ming bit CKP (SSPCON<4>). This then would give
waveforms for SPI communication as shown in
MSB is transmitted rst. In master mode, the SPI clock
rate (bit rate) is user programmable to be one of the fol-
lowing:
FOSC/4 (or TCY)
FOSC/16 (or 4 TCY)
FOSC/64 (or 16 TCY)
Timer2 output/2
This allows a maximum bit clock frequency (at 8 MHz)
of 2 MHz. When in slave mode the external clock must
meet the minimum high and low times.
In sleep mode, the slave can transmit and receive data
and wake the device from sleep.
FIGURE 11-4: SPI MASTER/SLAVE CONNECTION
Serial Input Buffer
(SSPBUF)
Shift Register
(SSPSR)
MSb
LSb
SDO
SDI
PROCESSOR 1
SCK
SPI Master SSPM3:SSPM0 = 00xxb
Serial Input Buffer
(SSPBUF)
Shift Register
(SSPSR)
LSb
MSb
SDI
SDO
PROCESSOR 2
SCK
SPI Slave SSPM3:SSPM0 = 010xb
Serial Clock
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