Mode 0
spim_clk
Mode 1
spim_clk
Mode 2
spim_clk
Mode 3
spim_clk
Sampling
Shift out
mcspi-009
Public Version
McSPI Functional Interface
www.ti.com
Table 20-3. SPI Master Clock Rates (continued)
Divider
Clock Rate
512
~93.7 kHz
1024
~46.8 kHz
2048
~23.4 kHz
4096
~11.7 kHz
8192
~5.8 kHz
16384
~2.9 kHz
32768
~1.5 kHz
–
Polarity and phase
The polarity (the SPIm.
[1] POL bit) and the phase (the
SPIm.
[0] PHA bit) of the SPI serial clock (spim_clk) are configurable to offer four
combinations. Software selects the right combination, depending on the device. See
and
Table 20-4. Phase and Polarity Combinations
Polarity (POL)
Phase (PHA)
SPI Mode
Comments
0
0
Mode 0
spim_clk is active high and sampling occurs on
the rising edge.
0
1
Mode 1
spim_clk is active high and sampling occurs on
the falling edge.
1
0
Mode 2
spim_clk is active low and sampling occurs on
the falling edge.
1
1
Mode 3
spim_clk is active low and sampling occurs on
the rising edge.
Figure 20-9. Phase and Polarity Combinations
20.3.3.1 Transfer Format
In both master and slave modes, McSPI drives the data lines when spim_csx is asserted.
Each word is transmitted starting with the most-significant bit (MSB).
This section explains the two cases of data transmission determined by the clock phase (PHA) and the
type of data transmission using a start-bit (SBE) called the start-bit mode:
•
Transmission in mode 0 and mode 2 (PHA = 0)
When PHA = 0, the first bit of the SPI word to transmit (on the master or the slave data output pin) is
valid one half cycle of spim_clk after the spim_csx assertion.
Therefore, the first edge of the spim_clk line is used by the master to sample the first data bit sent by
2984
Multichannel SPI
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated
Содержание OMAP36 Series
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