Motorola ColdFire MCF5281 - Manual (Page 418)

Queued Serial Peripheral Interface (QSPI)
22-14 Freescale Semiconductor
where QDLYR[DTL] has a range of 1–255. A zero value for DTL causes a delay-after-transfer value of
8192/f
sys
. Standard delay period (DT = 0) is calculated by the following:
Eqn. 22-4
Adequate delay between transfers must be specified for long data streams because the QSPI module
requires time to load a transmit RAM entry for transfer. Receiving devices need at least the standard delay
between successive transfers. If the internal bus clock is operating at a slower rate, the delay between
transfers must be increased proportionately.
22.4.4 Transfer Length
There are two transfer length options. The user can choose a default value of 8 bits or a programmed value
of 8 to 16 bits. The programmed value must be written into QMR[BITS]. The command RAM bits per
transfer enable field, QCR[BITSE], determines whether the default value (BITSE = 0) or the BITS[3–0]
value (BITSE = 1) is used. QMR[BITS] indicates the required number of bits to be transferred, with the
default value of 16 bits.
22.4.5 Data Transfer
The transfer operation is initiated by setting QDLYR[SPE]. Shortly after QDLYR[SPE] is set, the QSPI
executes the command at the command RAM address pointed to by QWR[NEWQP]. Data at the pointer
address in transmit RAM is loaded into the data serializer and transmitted. Data that is simultaneously
received is stored at the pointer address in receive RAM.
When the proper number of bits has been transferred, the QSPI stores the working queue pointer value in
QWR[CPTQP], increments the working queue pointer, and loads the next data for transfer from the
transmit RAM. The command pointed to by the incremented working queue pointer is executed next
unless a new value has been written to QWR[NEWQP]. If a new queue pointer value is written while a
transfer is in progress, the current transfer is completed normally.
When the CONT bit in the command RAM is set, the QSPI_CSn signals are asserted between transfers.
When CONT is cleared, QSPI_CSn are negated between transfers. The QSPI_CSn signals are not high
impedance.
When the QSPI reaches the end of the queue, it asserts the SPIF flag, QIR[SPIF]. If QIR[SPIFE] is set, an
interrupt request is generated when QIR[SPIF] is asserted. Then the QSPI clears QDLYR[SPE] and stops,
unless wraparound mode is enabled.
Wraparound mode is enabled by setting QWR[WREN]. The queue can wrap to pointer address 0x0, or to
the address specified by QWR[NEWQP], depending on the state of QWR[WRTO].
In wraparound mode, the QSPI cycles through the queue continuously, even while requesting interrupt
service. QDLYR[SPE] is not cleared when the last command in the queue is executed. New receive data
overwrites previously received data in the receive RAM. Each time the end of the queue is reached,
Standard delay after transfer
17
f
sys
------- (DT = 0) =
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3