MC33972 Datasheet, PDF (14/28 Pages) Motorola, Inc – Multiple Switch Detection Interface with Suppressed Wake-Up

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
Table 7. Wake-Up / Interrupt Command
Wake-Up /Interrupt Command
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 0 1 0 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0
0 0 0 0 0 0 1 1 X X sg13 sg12 sg11 sg10 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0
WETTING CURRENT REGISTER
The 33972 has two levels of switch contact current, 16 mA
and 2.0 mA (see Figure 10). The metallic command is used
to set the switch contact current level (Table 8). Programming
the metallic bit to logic [0] will set the switch wetting current to
2.0 mA. Programming the metallic bit to logic [1] will set the
switch contact wetting current to 16 mA. The MCU may
change or update the Wetting Current Register via software
at any time in Normal mode.
Wetting current is designed to provide higher levels of
current during switch closure. The higher level of current is
designed to keep switch contacts from building up oxides that
form on the switch contact surface.
Switch Contact Voltage
16 mA Switch Wetting Current
2.0 mA Switch Sustain Current
20 ms Wetting Current Timer
Figure 10. Contact Wetting and Sustain Current
Table 8. Metallic Command
Metallic Command
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 0 0 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0
0 0 0 0 0 1 0 1 X X sg13 sg12 sg11 sg10 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0
closed switch contact. With multiple wetting current timers
WETTING CURRENT TIMER REGISTER
Each switch input has a designated 20 ms timer. The timer
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
starts when the specific switch input crosses the comparator
threshold (4.0 V). When the 20 ms timer expires, the contact
allows the MCU to control the amount of time wetting current
is applied to the switch contact. Programming the wetting
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
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 (Table 9).
Table 9. 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 (Table 10). 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.
33972
14
Analog Integrated Circuit Device Data
Freescale Semiconductor