Motorola PowerQUICC II MPC8280 Series Reference Manual page 1367

Figure 39-6 shows the SPI transfer format in which SPICLK starts toggling at the
beginning of the transfer (SPMODE[CP] = 1).
SPICLK (CI = 0)
SPICLK (CI = 1)
SPIMOSI
(From Master)
SPIMISO
(From Slave)
SPISEL
NOTE: Q = Undefined Signal.
Figure 39-6. SPI Transfer Format with SPMODE[CP] = 1
39.4.1.1 SPI Examples with Different SPMODE[LEN] Values
The examples below show how SPMODE[LEN] is used to determine character length. To
help map the process, the conventions shown in Table 39-2 are used in the examples.
Convention
1
Both __ and _ are used to aid readability.
Once the data string image is determined, it is always transmitted byte by byte with the lsb
of the most-significant byte sent first. For all examples below, assume the memory contains
the following binary image:
msb ghij_klmn__opqr_stuv
Example 1
with LEN=4 (data size=5), the following data is selected:
msb xxxj_klmn__xxxr_stuv
with REV=0, the data string image is:
msb j_klmn__r_stuv
MOTOROLA
Freescale Semiconductor, Inc.
msb
Q msb
Table 39-2. Example Conventions
g–v
x
1
__
1
_
Chapter 39. Serial Peripheral Interface (SPI)
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Programming the SPI Registers
Description
Binary symbols
Deleted bit
Original byte boundary
Original 4-bit boundary.
lsb
lsb
lsb
lsb
lsb
39-9