MAC7200 datasheet(685/976 Pages) FREESCALE

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Functional Description

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

607

30.12.4.5 Peripheral Chip Select Strobe Enable (PCSS)

The PCSS signal provides a delay to allow the PCS signals to settle after transitioning thereby avoiding

glitches. When the DSPI is in Master Mode and PCSSE bit is set in the DSPI_MCR, PCSS provides a

signal for an external demultiplexer to decode the PCS[0] -PCS[4] and PCS[6] -PCS[7] signals into as

many as 128 glitch-free PCS signals. Figure 30-15 shows the timing of the PCSS signal relative to PCS

signals.

Figure 30-15. Peripheral Chip Select Strobe Timing

The delay between the assertion of the PCS signals and the assertion of PCSS is selected by the PCSSCK

field in the DSPI_CTAR based on the following formula:

Eqn. 30-6

At the end of the transfer the delay between PCSS negation and PCS negation is selected by the PASC field

in the DSPI_CTAR based on the following formula:

Eqn. 30-7

Table 30-28 shows an example of how to compute the tpcssck delay.

Table 30-29 shows an example of how to compute the tpasc delay.

The PCSS signal is not supported when Continuous Serial Communication SCK is enabled

(CONT_SCKE=1).

Table 30-27. Delay after Transfer Computation Example

PDT

Prescaler

Scaler

Fsys

Delay after Transfer

0b01

0b1110

32768

100 MHz

0.98 ms

Table 30-28. Peripheral Chip Select Strobe Assert Computation Example

PCSSCK

Prescaler

Fsys

Delay before Transfer

0b11

100 MHz

70.0 ns

Table 30-29. Peripheral Chip Select Strobe Negate Computation Example

PASC

Prescaler

Fsys

Delay after Transfer

0b11

100 MHz

70.0 ns

PCSSCK

PCSS

PCSx

PASC

PCSSCK

SYS

----------

PCSSCK

PASC

SYS

----------

PASC

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