18-2
MC9328MX1 Reference Manual
MOTOROLA
Serial Peripheral Interface Modules (SPI 1 and SPI 2)
Figure 18-1. SPI Module Block Diagram
18.2 Operation
To use the internal transmit (TX) and receive (RX) data FIFOs when the SPI 1 module is configured as a
master, two control signals are used for data transfer rate control: the SS signal (output) and the SPI_RDY
signal (input). The SPI 1 Sample Period Control Register (PERIODREG1) and the SPI 2 Sample Period
Control Register (PERIODREG2) also can be programmed to a fixed data transfer rate for either SPI 1 or
SPI 2.
When the SPI 1 module is configured as a slave, the user can configure the SPI 1 Control Register
(CONTROLREG1) to match the external SPI master’s timing. In this configuration, SS becomes an input
signal, and is used to latch data into or load data out to the internal data shift registers, as well as to
increment the data FIFO. Figure 18-2 on page 18-3 shows the generic SPI timing.
18.2.1 Phase and Polarity Configurations
The SPI master uses the SCLK signal to transfer data in and out of the shift register. Data is clocked by one
of four programmable clock phase and polarity combinations, selected through the phase (PHA) and
polarity (POL) bits in the CONTROLREG1 and CONTROLREG2 registers.
In Phase 0
operation (PHA=0) and SCLK Polarity active low (POL=0), output data changes on falling
edges of the SCLK signal and input data is shifted in on rising edges. The most significant bit (MSB) is
output when the CPU loads the transmitted data.
In Phase 0
operation (PHA=0) and SCLK Polarity active high (POL=1), output data changes on rising
edges of the SCLK signal and input data is shifted in on falling edges. The most significant bit (MSB) is
output on the first rising edge of the SCLK signal.
In Phase 1 operation (PHA=1) and SCLK Polarity active low (POL=0), output data changes on rising
edges of the SCLK signal and input data is shifted in on falling edges. The MSB is output on the first rising
edge of the SCLK signal.
In Phase 1 operation (PHA=1) and SCLK Polarity active high (POL=1), output data changes on falling
edges of the SCLK signal and input data is shifted in on rising edges. The MSB is output when the CPU
loads the transmitted data.
SS
IP BUS INTERFACE
MISO
MOSI
RX FIFO
SCLK
SPI_RDY
1
CLOCK
GENERATOR
CONTROL
SHIFT REGISTER
TX FIFO
1. SPI 2 module does not suppor
SPI_RDY control signal function.
Содержание DragonBall MC9328MX1
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Страница 86: ...2 18 MC9328MX1 Reference Manual MOTOROLA Signal Descriptions and Pin Assignments ...
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Страница 160: ...8 8 MC9328MX1 Reference Manual MOTOROLA System Control ...
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