Operation

The desired QSPI_CLK baud rate is related to the system clock and QMR[BAUD] by the following expression:

QMR[BAUD] = fSYS / [2 ⋅ (desired QSPI_CLK baud rate)]

Table 22-2. QSPI_CLK Frequency as Function of System Clock and Baud Rate

 

System Clock

 

 

QMR [BAUD]

66.67 MHz

 

 

2

16.5 MHz

 

 

4

8.25 MHz

 

 

8

4.125 MHz

 

 

16

2.063 MHz

 

 

32

1.031 MHz

 

 

255

129.4 kHz

 

 

22.4.3 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 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 = QDLYR[QCD]/fSYS QDLYR[QCD] has a range of 1–127.

When QDLYR[QCD] or QCR[DSCK] equals zero, the standard delay of one-half the QSPI_CLK period is used.

The command RAM delay after transmit enable bit, QCR[DT], 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. QCR[DT] 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:

MOTOROLA

Chapter 22. Queued Serial Peripheral Interface (QSPI) Module

22-7

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Motorola MCF5281, MCF5282 Transfer Delays, Qspiclk Frequency as Function of System Clock and Baud Rate, 66.67 MHz