6.3.2.1 Receive RAM
Data received by the QSPI is stored in this segment. The CPU reads this segment to
retrieve data from the QSPI. Data stored in receive RAM is right-justified. 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.
6.3.2.2 Transmit RAM
Data that is to be transmitted by the QSPI is stored in this segment. The CPU normally
writes one word of data into this segment for each queue command to be executed.
Information to be transmitted must be written to transmit RAM in a right-justified for-
mat. The QSPI cannot modify information in the transmit RAM. The QSPI copies the
information to its data serializer for transmission. Information remains in transmit RAM
until overwritten.
6
6.3.2.3 Command RAM
Command RAM is used by the QSPI in master mode. The CPU writes one byte of con-
trol information to this segment for each QSPI command to be executed. The QSPI
cannot modify information in command RAM.
Command RAM consists of 16 bytes. Each byte is divided into two fields. The periph-
eral chip-select field enables peripherals for transfer. The command control field pro-
vides transfer options.
A maximum of 16 commands can be in the queue. Queue execution by the QSPI pro-
ceeds from the address in NEWQP through the address in ENDQP (both of these
fields are in SPCR2).
6.3.3 QSPI Pins
The QSPI uses seven pins. These pins can be configured for general-purpose I/O
when not needed for QSPI application. When used for QSPI functions, the MOSI, MI-
SO, and SS pins should have pull-up resistors.
Table 6-2 shows QSPI input and output pins and their functions.
MOTOROLA
6-8
QUEUED SERIAL MODULE
MC68331
USER’S MANUAL
MOTOROLA [ MOTOROLA ]
