33972_09 Datasheet, PDF (19/32 Pages) Freescale Semiconductor, Inc – Multiple Switch Detection Interface with Suppressed Wake-up

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
Table 16. Serial Output (SO) Bit Data
Type of Input
Input
Programmed
Voltage on
Input Pin
SO SPI Bit
SP
Switch to Ground
SPn < 4.0V
1
Switch to Ground
SPn > 4.0V
0
Switch to Battery
SPn < 4.0V
0
Switch to Battery
SPn > 4.0V
1
SG
N/A
SGn < 4.0V
1
N/A
SGn > 4.0V
0
Table 17. Serial Output (SO) Response Register
SO Response Will
Always Send
them int
flg flg
SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SG13 SG12 SG11 SG10 SG9 SG8 SG7 SG6 SG5 SG4 SG3 SG2 SG1 SG0
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 (16 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 16 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 CS is LOW. The
maximum duration a switch state change can exist without
acknowledgement depends on the software response time to
the interrupt. Figure 6, page 9, shows the interaction
between changing input states and the INT and CS pins.
If desired the user may disable interrupts (wake up/
interrupt command) from the 33972 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 33972 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 33972 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 V_DD = 5.0 V and WAKE at
Logic [1])
• Falling edge of CS (with V_DD = 5.0 V)
• Power-ON Reset (POR)
The V_DD supply may be removed from the device during
Sleep mode. However removing V_DD 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, as shown in Table 18 The interrupt timer is
used as a periodic wake-up timer. When the timer expires, an
interrupt is generated and the device enters Normal mode.
Note The interrupt timer in the 33972 device may be
disabled by programming the interrupt bits to logic [1 1 1].
Table 19 shows the programmable settings of the Interrupt
timer.
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
0 0 0 0 1 1 0 0XXXXXXXXXX
Analog Integrated Circuit Device Data
Freescale Semiconductor
33972
19