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Analog Integrated Circuit Device Data
Freescale Semiconductor
21
33975
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
EXAMPLE OF NORMAL MODE OPERATION
The operation of the device in Normal mode is defined by the
states of the programmable internal control registers. A
typical application may have the following settings:
Programmable switch – set to switch-to-ground
All inputs set as wake-up
Wetting current on (32 mA)
Wetting current timer on (20 ms)
All inputs tri-state-disabled (comparator is active)
Analog select 00000 (no input channel selected)
With the device programmed as above, an interrupt will be
generated with each switch contact change of state (open-to-
close or close-to-open) and 32 mA of contact wetting current
will be source for 20 ms. The INT pin will remain low until
switch status is acknowledged by the microprocessor. It is
critical to understand INT will not be cleared on the rising
edge of CS if a switch closure occurs while the CS is low. The
maximum duration a switch state change can exist without
acknowledgement depends on the software response time to
between changing input states and the INT and CS pins.
If desired the user may disable interrupts (wake-up/interrupt
command) from the 33975 device and read the switch states
on a periodic basis. Switch activation and deactivation faster
than the MCU read rate will not be acknowledged.
The 33975 device will exit the Normal mode and enter the
Sleep mode only with a valid sleep command.
SLEEP MODE
Sleep mode is used to reduce system quiescent currents.
Sleep mode may be entered only by sending the sleep
command. All register settings programmed in Normal mode
will be maintained in Sleep mode.
The 33975 will exit Sleep mode and enter Normal mode when
any of the following events occur:
Input switch change of state (when enabled)
Interrupt timer expire
Falling edge of WAKE
Falling edge of INT (with VDD = 5.0 V and WAKE at
Logic [1])
Falling edge of CS (with VDD = 5.0 V)
Power-on reset (POR)
The VDD supply may be removed from the device during
Sleep mode. However removing VDD from the device in
Sleep mode will disable a wake-up from falling edge of INT
and CS.
Note: In cases where CS is used to wake the device, the first
SO data message is not valid.
The sleep command contains settings for two programmable
timers for Sleep mode, the interrupt timer and the scan timer,
Table 16. Serial Output (SO) Bit Data
Type of Input
Input
Programmed
Voltage on Input
Pin
SO SPI Bit
SP
Switch to Ground
SPn < 4.0 V
1
Switch to Ground
SPn > 4.0 V
0
Switch to Battery
SPn < 4.0 V
0
Switch to Battery
SPn > 4.0 V
1
SG
N/A
SGn < 4.0 V
1
N/A
SGn > 4.0 V
0
Table 17. Serial Output (SO) Response Register
SO Response
Will
Always Send
ther
m
flg
RST
flg
SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SG1
3
SG1
2
SG1
1
SG1
0
SG9 SG8 SG7 SG6 SG5 SG4 SG3 SG2 SG1 SG0
Table 18. Sleep Command
Sleep 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
1
0
X
int
timer
int
timer
int
timer
sca
ntimer
sca
ntimer
sca
ntimer