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MC68341 USER’S MANUAL
MOTOROLA
COMD.RAM consists of 16 bytes. Each byte is divided into two fields. The first, the
peripheral chip-select field, activates the correct serial peripheral during the transfer. The
second, the command control field, provides transfer options specifically for that
command/serial transfer. This feature gives the user more control over each transfer,
providing the flexibility to interface to external SPI chips with different requirements (refer
to Figure 9-5).
A maximum of 16 commands can be in the queue command control bytes. These bytes
are assigned an address from $0–$F. Queue execution by the QSPI proceeds from the
address contained in NEWQP through the address contained in ENDQP. Both of these
fields are contained in SPCR2.
COMD.RAM—Command RAM
$940
76543210
CONT
BITSE
DT
DSCK
RSVD
PCS1
PCS0 *
————————
CONT
BITSE
DT
DSCK
RSVD
PCS1
PCS0 *
$94F
COMMAND CONTROL
PERIPHERAL CHIP SELECT
*
The PCS0 bit represents the dual-function PCS0/SS .
Figure 9-5. Command RAM
CONT—Continue
1 = Keep peripheral chip selects asserted after transfer is complete.
0 = Return control of peripheral chip selects to QPDR after transfer is complete.
Some peripheral chips must be deselected between every QSPI transfer. Other chips
must remain selected between several sequential serial transfers. CONT is designed to
provide the flexibility needed to handle both cases.
If CONT = 1 and the peripheral-chip-select pattern for the next command is the same as
that of the present command, the QSPI drives the PCS pins to the same value
continuously during the two serial transfers. An unlimited number of serial transfers may
be sent to the same peripheral(s) without deselecting it (them) by setting CONT = 1.
If CONT = 1 and the peripheral-chip-select pattern for the next command is different
from that of the present command, the QSPI drives the PCS pins to the new value for
the second serial transfer. Although this case is similar to CONT = 0, a difference
remains. When CONT = 1, the QSPI continues to drive the PSC pins using the pattern
from the first transfer until it switches to using the pattern for the second transfer.
When CONT = 0, the QSPI drives the PCS pins to the values found in register QPDR
between serial transfers.
BITSE—Bits Per Transfer Enable
1 = Number of bits set in BITS field of SPCR0
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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