mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 345

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

MOTOROLA
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:
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:
where QDLYR[DTL] has a range of 1–255.
Table 14-2. QSPI_CLK Frequency as Function of CPU Clock and Baud Rate
Delay after transfer = 32 × QDLYR[DTL] /CLKIN frequency (DT = 1)
QMR [BAUD]
255
16
32
2
4
8
QSPI_CS-to-QSPI_CLK delay = QCD/CLKIN frequency
Chapter 14. Queued Serial Peripheral Interface (QSPI) Module
16,500,000
8,250,000
4,125,000
2,062,500
1,031,250
129,412
66 MHz
12,000,000
6,000,000
3,000,000
1,500,000
750,000
48 MHz
94,118
CPU Clock
8,250,000
4,125,000
2,062,500
1,031,250
515,625
33 MHz
64,706
5,000,000
2,500,000
1,250,000
625,000
312,500
20 MHz
39,216
Operation
14-7