MAC7200 datasheet(858/976 Pages) FREESCALE

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Initialization/Application Information

MAC7200 Microcontroller Family Reference Manual, Rev. 2

780

Freescale Semiconductor

To compensate temperature influences it is recommended to do the calibration e.g. every 100 .. 500ms

especially when the device is heating up. The calibration frequency might be reduced when the

temperature is expected to be stable.

33.12.2.3.1

Sample Special Channel 75% x (VRH -VRL)

To sample this channel a command word with the value 0x638B must be written to ATDCW. Table 33-21

shows of what settings this value is composed:

When the conversion finished (CC flag is set) the result can be read. To reduce the influence on the

conversion result caused by noise on the ATD supply pins this conversion should be repeated several times.

Depending on the result variance the mean or median can be used.

NOTE

When converting this special channel the predischarge feature must be

enabled to reduce the influence of parasitic charges. The predischarge time

can be two ATD clock cycles or higher.

33.12.2.3.2

Sample Special Channel 25% x (VRH -VRL)

To sample this channel a command word with the value 0x638C must be written to ATDCW. This value

represents the bit values shown in Table 33-21 but CWCH = 0b0_1100.

When the conversion finished (CC flag is set) the result can be read. To reduce the influence on the

conversion result caused by noise on the ATD supply pins this conversion should be repeated several times.

Depending on the result variance the mean or median can be used.

NOTE

When converting this special channel the predischarge feature must be

enabled to reduce the influence of parasitic charges. The predischarge time

can be two ATD clock cycles or higher.

Table 33-21. Command Word #1 to Determine Gain and Offset

Bit(s)

Value

Description

CWAR

0b0

use raw conversion result

CWSC

0b1

special channel

CWGI

0b1

Generate an interrupt

CWCM

0b00

Continuous conversion

CWSL

0b01

Eight ATD clock cycles sampling time

CWNF

0b1100

right justified unsigned, 12 bit

CWCH

0b0_1011

special channel 75% x (VRH -VRL)

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