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signals in CPU bus mode (including being active low). At the same time, the slave transmits the byte
enable values of the previous access on
SPI_MISO.The next 24 bits the master transmits on
SPI_MOSI are address bits, starting from A24 (MSB) and ending
with A1 (LSB). At the same time, the slave transmits the address bits of the previous access on
SPI_MISO.
The next 32 bits the master transmits on
SPI_MOSI are 32 bits of data, starting from D31 (MSB) and
ending with D0 (LSB). At the same time, the slave transmits 32 don’t-care bits on
SPI_MISO.Finally the master transmits 8 don’t care bits on
SPI_MOSI. During these clock periods the slave transmits
th bit is a status bit that indicates
whether the last access was completed successfully (1) or is still in progress (0). The 0 value indicates that
the current operation has not yet completed and that the status command must follow (see section
The master ends the write access by deasserting
SPI_SEL_N.
The total number of
SPI_CLK cycles for a write command is 72. This is summarized in
Table 10-2.Table 10-2. SPI Write Command Sequence
Bit Number
SPI_MOSI
SPI_MISO
1
Reserved
2–3
opcode 01 (write)
Previous access opcode
4
H_WR_BE3_N value
Previous access H_WR_BE3_N value
5
H_WR_BE2_N value
Previous access H_WR_BE2_N value
6
H_WR_BE1_N value
Previous access H_WR_BE1_N value
7
H_WR_BE0_N value
Previous access H_WR_BE0_N value
8
Reserved
9–32
Address [24 to 1]
Previous access address [24 to 1]
33–64
Data (32 bits)
Don’t care (32 bits)
65–71
Don’t care (7 bits)
Idle (7 bits)
72
Don’t care (1 bit)
Status bit: 1=access has finished, 0=access has not finished
10.3.4.2 Read Command
The SPI read command proceeds as follows:
The SPI master (CPU) starts a write access by asserting
SPI_SEL_N (low).
Then, during each
SPI_CLK cycle a
SPI_MOSI data bit is transmitted by the master (CPU), while a
SPI_MISO bit is transmitted by the slave (the device).
The master then transmits two opcode bits on
SPI_MOSI. These bits specify a read, write or status
command. The value 10b represents a read command. At the same time, the slave transmits the opcode
The next four bits the master transmits on
SPI_MOSI are byte-enable values: byte_en_3, byte_en_2,