33993 datasheet(14/28 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33993

FUNCTIONAL DEVICE OPERATION

LOGIC COMMANDS AND REGISTERS

WETTING CURRENT TIMER REGISTER

Each switch input has a designated 20 ms timer. The timer

starts when the specific switch input crosses the comparator

threshold (4.0 V). When the 20 ms timer expires, the contact

current is reduced from 16 mA to 2.0 mA. The wetting current

timer may be disabled for a specific input. When the timer is

disabled, 16 mA of current will continue to flow through the

closed switch contact. With multiple wetting current timers

disabled, power dissipation for the IC must be considered.

The MCU may change or update the Wetting Current

Timer Register via software at any time in Normal mode. This

allows the MCU to control the amount of time wetting current

is applied to the switch contact. Programming the wetting

current timer bit to logic [0] will disable the wetting current

timer. Programming the wetting current timer bit to logic [1]

will enable the wetting current timer (refer to Table 8).

TRI-STATE REGISTER

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

node as high impedance (refer to Table 9). By setting the

Tri-State Register bit to logic [1], the input will be high

impedance 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

ANALOG SELECT REGISTER

The analog voltage on switch inputs may be read by the

MCU using the analog command (refer to Table 10). 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 (refer to Table 10). The

analog command does not allow pull-down currents on the

SPn inputs. Setting the current to 16 mA 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 20. The MCU may change or update the

Table 7. Metallic Command

Metallic Command

Command Bits

sp7

sp6

sp5

sp4

sp3

sp2

sp1

sp0

sg1

sg9

sg8

sg7

sg6

sg5

sg4

sg3

sg2

sg1

sg0

Table 8. Wetting Current Timer Enable Command

Wetting Current Timer Commands

Command Bits

sp7

sp6

sp5

sp4

sp3

sp2

sp1

sp0

sg1

sg9

sg8

sg7

sg6

sg5

sg4

sg3

sg2

sg1

sg0

Table 9. Tri-State Command

Tri-State Commands

Command Bits

sp7

sp6

sp5

sp4

sp3

sp2

sp1

sp0

sg1

sg9

sg8

sg7

sg6

sg5

sg4

sg3

sg2

sg1

sg0

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