ADC 320F Especificações descarregar pdf (Página 22)

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25 µs

50 µs

ePWM

counter

PWM A/B

output

, I

, V

, I

, V

Uninterrupted Autosequenced Mode

Example 1-4. Sequencer Start/Stop Operation

Requirement: To start three autoconversions (e.g., I

) off trigger 1 (underflow) and three

autoconversions (e.g., V

) off trigger 2 (period). Triggers 1 and 2 are separated in time by 25 µs

and are provided by an ePWM. See Figure 1-7 . Only SEQ1 is used in this case.

Note: Triggers 1 and 2 may be an SOC signal from ePWM, external pin, or software. The same

trigger source may occur twice to satisfy the dual-trigger requirement of this example.

Care must be taken such that multiple ePWM triggers are not lost due sequences already

in progress. See Section 1.3.3 .

Here MAX_CONV1 is set to 2 and the ADC Input Channel Select Sequencing Control Registers

(ADCCHSELSEQn) are set as shown in Table 1-4 .

Once reset and initialized, SEQ1 waits for a trigger. With the first trigger, three conversions with

channel-select values of: CONV00 (I

), CONV01 (I

), and CONV02 (I

) are performed. SEQ1 then waits

at current state for another trigger. Twenty-five microseconds later when the second trigger arrives,

another three conversions occur, with channel-select values of CONV03 (V

), CONV04 (V

), and

CONV05 (V

The value of MAX_CONV1 is automatically loaded into SEQ_CNTR for both trigger cases. If a different

number of conversions are required at the second trigger point, you must (at some appropriate time

before the second trigger) change the value of MAX_CONV1 through software, otherwise, the current

(originally loaded) value will be reused. This can be done by an ISR that changes the value of

MAX_CONV1 at the appropriate time. The interrupt operation modes are described in Section 1.3.4 .

At the end of the second autoconversion session, the ADC result registers will have the values shown

in Table 1-5 .

At this point, SEQ1 keeps "waiting" at the current state for another trigger. Now, the user can reset

SEQ1 (by software) to state CONV00 and repeat the same trigger1, 2 sessions.

Figure 1-7. Example of ePWM Triggers to Start the Sequencer

22 Analog-to-Digital Converter (ADC) SPRU812A – September 2007 – Revised October 2007

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