MC33993 Datasheet, PDF (14/28 Pages) Motorola, Inc – Multiple Switch Detection Interface

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 4).
Table 4. Wetting Current Timer Enable Command
Wetting Current Timer Commands
Command Bits
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 0 0 0 0 1 1 1 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0
0 0 0 0 1 0 0 0 X X sg13 sg12 sg11 sg10 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0
Tri-State Register
The tri-state command is use to set the SPn or SGn input
node as high impedance (refer to Table 5). 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 Register via
software at any time in Normal mode.
Table 5. Tri-State Command
Tri-State Commands
Command Bits
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 0 0 0 1 0 0 1 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0
0 0 0 0 1 0 1 0 X X sg13 sg12 sg11 sg10 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0
33993/D
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MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA