Chapter 14. Queued Serial Peripheral Interface (QSPI) Module
14-7
Operation
14.4.3 Transfer Delays
The QSPI supports programmable delays for the QSPI_CS signals before and after a
transfer. The time between QSPI_CS assertion and the leading QSPI_CLK edge, and the
time between the end of one transfer and the beginning of the next, are both independently
programmable.
The chip select to clock delay enable (DSCK) bit in command RAM, QCR[DSCK], enables
the programmable delay period from QSPI_CS assertion until the leading edge of
QSPI_CLK. QDLYR[QCD] determines the period of delay before the leading edge of
QSPI_CLK. The following expression determines the actual delay before the QSPI_CLK
leading edge:
QSPI_CS-to-QSPI_CLK delay = QCD/CLKIN frequency
QCD has a range of 1–127.
When QCD or DSCK equals zero, the standard delay of one-half the QSPI_CLK period is
used.
The delay after transmit enable (DT) bit in command RAM enables the programmable
delay period from the negation of the QSPI_CS signals until the start of the next transfer.
The delay after transfer can be used to provide a peripheral deselect interval. A delay can
also be inserted between consecutive transfers to allow serial A/D converters to complete
conversion. There are two transfer delay options: the user can choose to delay a standard
period after serial transfer is complete or can specify a delay period. Writing a value to
QDLYR[DTL] specifies a delay period. The DT bit in command RAM determines whether
the standard delay period (DT = 0) or the specified delay period (DT = 1) is used. The
following expression is used to calculate the delay:
Delay after transfer = 32
×
QDLYR[DTL] /CLKIN frequency (DT = 1)
where QDLYR[DTL] has a range of 1–255.
Table 14-2. QSPI_CLK Frequency as Function of CPU Clock and Baud Rate
CPU Clock
QMR [BAUD]
66 MHz
48 MHz
33 MHz
20 MHz
1
33,000,000
24,000,000
16,500,000
10,000,000
2
16,500,000
12,000,000
8,250,000
5,000,000
4
8,250,000
6,000,000
4,125,000
2,500,000
8
4,125,000
3,000,000
2,062,500
1,250,000
16
2,062,500
1,500,000
1,031,250
625,000
32
1,031,250
750,000
515,625
312,500
255
129,412
94,118
64,706
39,216
Содержание DigitalDNA ColdFire MCF5272
Страница 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
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Страница 58: ...1 10 MCF5272 User s Manual MCF5272 Specific Features ...
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