Motorola MPC8260 - Manual (Page 932)

33-8 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part IV. Communications Processor Module
33.4.1.1 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 33-2 are used in the examples.
Once the data string image is determined, it is always transmitted byte by byte with the lsb
of the most-signiÞcant byte sent Þrst. For all examples below, assume the memory contains
the following binary image:
msb ghij_klmn__opqr_stuv lsb
Example 1
with LEN=4 (data size=5), the following data is selected:
msb xxxj_klmn__xxxr_stuv lsb
with REV=0, the data string image is:
msb j_klmn__r_stuv lsb
the order of the string appearing on the line, a byte at a time is:
first nmlk_j__vuts_r last
with REV=1,the string has each byte reversed, and the data string image is:
msb nmlk_j__vuts_r lsb
the order of the string appearing on the line, one byte at a time is:
first j_klmn__r_stuv last
Example 2
with LEN=7 (data size=8), the following data is selected:
msb ghij_klmn__opqr_stuv lsb
the data string is selected:
msb ghij_klmn__opqr_stuv lsb
with REV=0, the string transmitted, a byte at a time with lsb first is:
first nmlk_jihg__vuts_rqpo last
with REV=1, the string is byte reversed and transmitted, a byte at a time, with
lsb first:
first ghij_klmn__opqr_stuv last
Example 3:
with LEN=0xC (data size=13), the following data is selected:
msb ghij_klmn__xxxr_stuv lsb
Table 33-2. Example Conventions
Convention Description
gÐv Binary symbols
x Deleted bit
__ 1
1 Both __ and _ are used to aid readability.
Original byte boundary
_ 1 Original 4-bit boundary.