MAC7200 datasheet(818/976 Pages) FREESCALE

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ATD Application Usage

MAC7200 Microcontroller Family Reference Manual, Rev. 2

740

Freescale Semiconductor

•

DMA request fo r command word is asserted immediately after module is turned on

33.7

ATD Application Usage

33.7.1

Enabling the ATD

Before the ATD can be used, it must be explicitly enabled by clearing the MDIS bit.

33.7.2

Setting up the ATD

In order to use the basic functionality of the ATD, it is only necessary to clear the MDIS bit. Since all

analog inputs on the MAC72xx are routed directly through the PIM to the ATD, it is not necessary to set

up the PIM in order to use the ATD to sample channels. In this case, you can use a pin both as an analog

input for the ATD and as digital General Purpose Input. These pins can not be used as General Purpose

Outputs.

33.7.3

Using external triggers

If you want to use the external triggering capability of the ATD, you should use the following steps:

1. Configure the appropriate pin(s) to be in Peripheral Mode, in the CONFIG register(s) in the PIM

2. Clear the MDIS bit in the ATD

3. Write the ATDETRIGCH register in the ATD to set the desired channel number

4. Write ‘11’ to the TRIGSEL bits in the ATDTRIGCTL register in the ATD

33.7.4

Using the system triggers

If the ATD should start conversions synchronous to SYSTRIG0 or SYSTRIG1 the following settings must

be done in the PIT:

1. PIT: Clear MDIS bit

2. PIT: Specify timer reload value

3. PIT: Enable timer

The timer reload value for step PIT2) can be calculated with the following formula:

Eqn. 33-1

33.7.4.1

Example — Using System Triggers

The system clock is66.67Mhz (TSYSCLOCK = 15ns), which gives us a bus clock of 40Mhz (TBUSCLOCK =

30ns). The desired trigger period is 30

μs.

Eqn. 33-2

TriggerPeriod

ClockPeriod

----------------------------------------

TimerReloadValue

–

TriggerPeriod

ClockPeriod

----------------------------------------

30us

30ns

-------------

–

999

0x000003e7

–

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