COP8-REF-AM datasheet(50/83 Pages) NSC

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15.0 A/D Converter (Continued)

TABLE 22. A/D Converter Channel Selection when the Multiplexor Output is Disabled

Select Bits

Mode Select

ADMOD = 0

Single Ended

Mode

Mode Select

ADMOD = 1

Differential

Mode

Mux Output

Disabled

ADCH3

ADCH2

ADCH1

ADCH0

Channel No.

Channel Pairs

(+, −)

MUX

Temp sensor, if

enabled

Not used

10, 11 (Note 12)

11, 10 (Note 12)

12, 13 (Note 12)

13, 12 (Note 12)

14, 15 (Note 12)

15, 14 (Note 12)

Note 12: Only if the programmable gain amplifier is bypassed.

15.1.1.2 Multiplexor Output Select

The MUX bit field allows the output of the A/D multiplexor

(with the exception of the temperature sensor channel) and

the input to the A/D to be connected directly to external pins.

This allows for an external, common filter/signal conditioning

circuit to be applied to all channels. The output of the exter-

nal conditioning circuit can then be connected directly to the

input of the Sample and Hold input on the A/D Converter.

See Figure 26 for the single ended mode diagram. The

Multiplexor output is connected to ADCH4 and the A/D input

is connected to ADCH5. For differential mode, the differential

multiplexor outputs are available and should be converted to

a single ended voltage for connection to the A/D Converter

Input. The programmable gain amplifier must be bypassed

when using the multiplexor output feature in differential

mode. See Figure 27.

The channel assignments for this mode are shown in Table

23.

When using the Mux Output feature, the delay though the

internal multiplexor to the pin, plus the delay of the external

filter circuit, plus the internal delay to the Sample and Hold

will exceed the three clock cycles that’s allowed in the con-

version. This requires that whenever the MUX bit = 1, that

the channel selected by ADCH3:0 bits, be enabled, even

when ADBSY = 0, and gated to the mux output pin. The input

path to the A/D converter should also be enabled. This

allows the input channel to be selected and settled before

starting a conversion. The sequence to perform conversions

using the Mux Out feature is a multistep process and is listed

below.

Select the desired channel, excluding the temperature

sensor channel, and operating modes and load them

into ENAD without setting ADBSY.

Wait the appropriate time until the analog input has

settled. This will depend on the application and the

response of the external circuit.

Select the same desired channel and operating modes

used in step 1 and load them into ENAD and also set

ADBSY. This will start the conversion.

After conversion is completed, obtain the results from

the result registers.

20006356

FIGURE 26. A/D with Single Ended Mux Output Feature

Enabled

20006357

FIGURE 27. A/D with Differential Mux Output Feature

Enabled

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