33972 datasheet(16/32 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33972

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

TRI-STATE REGISTER

The tri-state command is use to set the SPn or SGn input

node as high-impedance (Table 10). By setting the tri-state

regardless of the metallic command setting. The comparator

on each input remains active. This command allows the use

of each input as a comparator with a 4.0 V threshold. The

MCU may change or update the tri-state register via software

at any time in Normal mode.

ANALOG SELECT REGISTER

The analog voltage on switch inputs may be read by the

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

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

selected input pin is buffered and made available on the

AMUX output pin. The AMUX output pin is clamped to a

maximum of VDD volts regardless of the higher voltages

present on the input pin. 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 (16 mA,

2.0 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 2.0 mA, and 1,0 selects 16 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 (Table 11). The analog

command does not allow pull-down currents on the SPn

inputs. Setting the current to 16 or 2.0 mA may be useful for

reading sensor inputs. Further information is provided in the

Typical Applications section of this datasheet beginning on

page 21. The MCU may change or update the analog select

Table 10. Tri-State Command

Tri-State Commands

Command Bits

sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0

sg13 sg12 sg11 sg10 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0

Table 11. Analog Command

Analog Command

Not used

Current Select Analog Channel Select

16 mA 2.0 mA

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