MAC7200 datasheet(867/976 Pages) FREESCALE

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Initialization/Application Information

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

789

33.12.3.6 Example 6: Queue Running Idle

This example shows a conversion sequence where the command words are not delivered in time and

therefore the sequence stagnates. This can happen e.g. due to DMA performance issues.

In this sequence all command words use the same setting:

•CMD #n: CWCW = “continuous conversion”

The ATD will execute conversions as long as there is a command word in the ATDCC register. Command

cmd #1 and cmd #2 are executed normally. As after cmd #2 there is no new command word available the

ATD will wait until cmd #3 arrives. Once cmd #3 was written to ATDCW and pushed to ATDCC the

conversion sequence can continue.

Figure 33-34 shows the described sequence:

Figure 33-34. Conversion Procedure for Example 6

33.12.3.7 Example 7: Entering Low-power Mode During a Conversion

This example shows a conversion sequence which gets interrupted as a low-power mode is entered. In this

sequence all command words use the same setting:

•CMD #n: CWCW = “continuous conversion”

The first conversion is started as usual: there is a DMA request for a command word and therefore the

DMA writes cmd #1 to ATDCW which is pushed to ATDCC. At the end of the conversion the result is

pushed to ATDRR. After this the second conversion starts (cmd #2).

During the second conversion the system enters low-power mode (LP-mode). The conversion is

terminated immediately and the command word cmd #3 in ATDCW is discarded. ATDCC and ATDCW

are both empty. Nevertheless no DMA request for a command word (RX request) is asserted.

The conversion result (rst #1), which has not been read before low-power mode was entered, is still

available in the result register and therefore the DMA request (TX request) remains asserted.

After low-power mode is left a request for a new command word is immediately asserted. But as the analog

conversion circuit was disabled during low-power mode no new conversions are allowed to start until the

recovery time tREC elapsed. This is why cmd #4 is written to ATDCW after tREC elapsed. The conversions

started after that time (cmd #4 and cmd #5) are executed normally.

In this example the conversion result rst #1 is read after low-power mode was left. This was done to

illustrate that the TX request is not affected by the low-power mode. It would have been possible to read

ATDRR before entering low-power mode.

empty

cmd #2

cmd #1

empty

RX request

Write ATDCW

ATDCW

ATDCC

ATDRR

rst #3

cmd #4

cmd #2

cmd #3

rst #1

rst #2

empty

#3 empty

cmd #4

cmd #5

empty

CSM

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