MAC7200 datasheet(863/976 Pages) FREESCALE

863 / 976 page

Initialization/Application Information

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

785

Figure 33-28. Conversion Procedure for Example 2

To make the ATD fetch new command words it is required to write another command word to ATDCW

(cmd #4). As this command word has CWCM = “convert continuously” another command word is

requested.

The conversion sequence cmd #4 and cmd #5 will be executed in the same way like for cmd #1 to cmd #2.

33.12.3.3 Example 3: Interrupted Conversion Sequence

This example will show how a continuous conversion can be interrupted. Again for simplification all but

the CWCM bits are disregarded:

•

CMD #1, CMD #2, CMD #3: CWCM = “continuous conversion”

•

CMD #4: CWCM = “conversion reset”

When the first conversion is started according to example 2 (CSM goes from C1 to C3 and finally to C4)

the ATD will keep switching between the states C3 and C4 as long as new command words with CWCM =

“continuous conversion” are written to ATDCW. In this example this is true for command #1 and #2

(cmd #1 and cmd #2). The result of each conversion is saved in the same way as described in example 2.

After the third conversion (cmd #3) started the next command (cmd #4) is written to ATDCW.

Immediately after the write access the third conversion is terminated. It is irrelevant whether the current

CSM state was C3 or C4 or C2 (as explained in Section 33.12.3.4, “Example 4: Edge-triggered

Conversion”). The CSM will always move to state C1 (See Figure 33-17).

If the conversion is terminated while a DMA request for a result is pending (the RSM is in state R2) this

DMA request remains asserted until ATDRR was read.

In Figure 33-29 the conversion procedure for this example is shown:

empty

cmd #2

cmd #1

cmd #2

cmd #3

empty

cmd #3

empty

rst #1

rst #3

rst #2

empty

#4 empty

cmd #5

cmd #4

empty

rst #4

cmd #5

RX request

Write ATDCW

ATDCW

ATDCC

ATDRR

TX request

Read ATDRR

Conv. complete

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