MC1321x Serial Peripheral Interface (SPI)
MC1321x Reference Manual, Rev. 1.6
4-2
Freescale Semiconductor
4.2
Features
Features of the SPI bus interface:
•
MCU bus master
•
Modem bus slave
•
Bi-directional data transfer
•
Dedicated interface; must meet modem protocol requirements
•
Programmable SPI clock rate; maximum rate is 8 MHz
•
Double-buffered transmit and receive at MCU
•
Serial clock phase and polarity must meet modem requirements (MCU control bits CPHA = 0 and
CPOL = 0)
•
Slave select programmed to meet modem protocol
•
MSB-first shifting
4.3
SPI System Block Diagram
This section shows the system level diagram for the SPI.
shows the SPI modules of the MCU
and modem in the master-slave arrangement.
Figure 4-2. SPI System Block Diagram
The MCU (master) initiates all SPI transfers. During a transfer, the master shifts data out (on the MOSI
pin) to the slave while simultaneously shifting data in (on the MISO pin) from the slave. Although the SPI
interface supports simultaneous data exchange between master and slave, the modem SPI protocol only
uses data exchange in one direction at a time. The SPSCK signal is a clock output from the master and an
input to the slave. The slave device must be selected by a low level on the slave select input (SS1 pin).
7
6
5
4
3
2
1
0
SPI SHIFTER
CLOCK
GENERATOR
7
6
5
4
3
2
1
0
SPI SHIFTER
PTE2/SS1
SPSCK1
MISO1
MOS1
CE
SPICLK
MISO
MOSI
MCU (MASTER)
MODEM (SLAVE)
Содержание freescale semiconductor MC13211
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