33975 datasheet(17/32 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33975

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

ANALOG SELECT REGISTER

The analog voltage on switch inputs may be read by the

MCU using the analog command (refer to Table 11). Internal

to the IC is a 22-to-1 analog multiplexer. The voltage present

on the selected input terminal is buffered and made available

on the AMUX output terminal. The AMUX output terminal is

clamped to a maximum of VDD volts regardless of the higher

voltages present on the input terminal. After an input has

been selected as the analog, the corresponding bit in the next

SO data stream will be logic [0]. When selecting a channel to

be read as analog, the user must also set the desired current

(32 mA, 4.0 mA, or high impedance). Setting bit 6 and bit 5 to

0,0 selects the input as high impedance. Setting bit 6 and

bit 5 to 0,1 selects 4.0 mA, and 1,0 selects 32 mA. Setting

bit 6 and bit 5 to 1,1 in the Analog Select Register is not

allowed and will place the input as an analog input with high

impedance.

Analog currents set by the analog command are pull-up

currents for all SGn and SPn inputs (refer to Table 11). The

analog command does not allow pull-down currents on the

SPn inputs. Setting the current to 32 mA or 4.0 mA may be

useful for reading sensor inputs. Further information is

provided in the Typical Applications section of this datasheet

beginning on page 22. The MCU may change or update the

Analog Select Register via software at any time in Normal

mode.

Table 11. Analog Command

Analog Command

Not used

Current

Select

Analog Channel Select

4.0

Table 12. Analog Channel

Bits 43210

Analog Channel Select

00000

No Input Selected

00001

SG0

00010

SG1

00011

SG2

00100

SG3

00101

SG4

00110

SG5

00111

SG6

01000

SG7

01001

SG8

01010

SG9

01011

SG10

01100

SG11

01101

SG12

01110

SG13

01111

SP0

10000

SP1

10001

SP2

10010

SP3

10011

SP4

10100

SP5

10101

SP6

10110

SP7

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