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MOTOROLA
MC68341 USER’S MANUAL
9- 27
REC.RAM
TRAN.RAM
D00
D1E
D20
D3E
WORD
D40
D4F
COMD.RAM
BYTE
0
F
ENTRY
WORD
Figure 9-4. Organization of the QSPI RAM
Once the CPU has set up the queue of QSPI commands and enabled the QSPI, the QSPI
operates independently of the CPU. The QSPI executes all of the commands in its queue,
sets a flag indicating that it is finished, and then either interrupts the CPU or waits for CPU
intervention.
9.5.4.6.1 Receive Data RAM (REC.RAM). This segment of the RAM stores the data that
is received by the QSPI from peripherals, SPI bus masters, or other SPI devices. The
CPU reads this segment of RAM to retrieve the data from the QSPI. Data stored in receive
RAM is right-justified, i.e., the least significant bit is always in the right-most bit position
within the word (bit 0) regardless of the serial transfer length. Unused bits in a receive
queue entry are set to zero by the QSPI upon completion of the individual queue entry.
The CPU can access the data using byte, word, or long-word addressing.
The CPTQP value in SPSR shows which queue entries have been executed. The CPU
uses this information to determine which locations in receive RAM contain valid data
before reading them.
9.5.4.6.2 Transmit Data RAM (TRAN.RAM) . This segment of the RAM stores the data
that is to be transmitted by the QSPI to peripherals. The CPU normally writes one word of
data into this segment for each queue command to be executed. If the corresponding
peripheral, such as a serial input port, is used solely to input data, then this segment does
not need to be initialized.
Information to be transmitted by the QSPI should be written by the CPU to the transmit
data segment in a right-justified manner. The information in the transmit data segment of
the RAM cannot be modified by the QSPI. The QSPI merely copies the information to its
data serializer for transmission to a peripheral. Information in transmit RAM remains there
until it is re-written by the CPU.
9.5.4.6.3 Command RAM (COMD.RAM). The command segment of the QSPI RAM is
used only by the QSPI when it is in master mode. The CPU writes one byte of control
information to this segment for each QSPI command to be executed. The information in
the command RAM cannot be modified by the QSPI. It merely uses the information to
perform the serial transfer.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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