MAC7200 datasheet(845/976 Pages) FREESCALE

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Functional Description

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

767

On completion of a conversion the value of the CWCM bits of the current command in ATDCC will

determine how the ATD will continue:

When a conversion finished, the ATD expects the ATDRR to be read. Therefore it will assert a DMA

request. This action is independent of the value of CWCM, and runs in parallel to the conversion process

(see Figure 33-17). If the result has been read the DMA request is deasserted.

It is not possible for the conversion in progress to have a command word with CWCM=00. This is because

writing a command word with this bit value to the ATDCW register will immediately stop any conversion.

While a conversion is running, the ATD will try to get a new command word by asserting a DMA request.

When a new command word is written to the ATDCW (either by the DMA or the core) the DMA request

is deasserted. This scheme allows a new command word to be available before the current conversion

finishes.

The ATD module does not distinguish between an access by the DMA and an access by the MCU. Both

can have access to the ATDCW or the ATDRR registers but only one at the same time.

The following two figures show the conversion process in more detail. As previously mentioned, saving

results (see Figure 33-18a), fetching commands (see Figure 33-18b) and performing conversions (see

Figure 33-17) are independent of each other, and are therefore split into three separate descriptions, shown

in the following figures.

Table 33-19. Conversion Start Behavior

CWCM

Behavior

“conversion reset”: Writing such a command word to the command register ATDCW will immediately abort the current

conversion. All bits in the command word beside the CWCM bits are ignored.

If the aborted conversion was either “convert continuously” or “wait for trigger” the ATD will assert a DMA request for

a new command. If the aborted conversion was “convert then pause” the ATD will not assert a DMA request for a new

command. The DMA request for saving the conversion result remains unaffected in both cases.

“convert then pause”: The ATD will start a conversion immediately after the command word has been written to

ATDCW and the previous conversion, if any, finished.

“wait for trigger”: The ATD will start a conversion only when the previous conversion, if any, finished and a trigger has

been asserted. The trigger definition will be explained later.

“convert continuously”: The ATD will start a conversion immediately after the command word has been written to

ATDCW and the previous conversion, if any, finished.

Table 33-20. Conversion Continue Behavior

CWCM

Behavior

- Not applicable -

The ATD will do nothing but wait. A new conversion will not be started.

The ATD will try to start a new conversion. However, this can only be done if there is a new command word available.

If this is the case a new conversion can (according to this command word) start. If not, the ATD will continue waiting

for a new command.

The ATD will try to start a new conversion. However, this can only be done if there is a new command word available.

If this is the case a new conversion can (according to this command word) start. If not, the ATD will continue waiting

for a new command.

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