33975 Datasheet, PDF (18/32 Pages) Freescale Semiconductor, Inc – Multiple Switch Detection Interface with Suppressed Wake-Up and 32mA Wetting Current

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
CALIBRATION OF TIMERS
In cases where an accurate time base is required, the user
may calibrate the internal timers using the calibration
command (refer to Table 13). After the 33975 device
receives the calibration command, the device expects 512 µs
logic [0] calibration pulse on the CS terminal. The pulse is
used to calibrate the internal clock. No other SPI terminals
should transition during this 512 µs calibration pulse.
Table 13. Calibration Command
Because the oscillator frequency changes with temperature,
calibration is required for an accurate time base. Calibrating
the timers has no affect on the quiescent current
measurement. The calibration command simply makes the
time base more accurate. The calibration command may be
used to update the device on a periodic basis. All reset
conditions clear the calibration register and places the device
in the uncalibrated state.
Calibration 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 0 1 1XXXXXXXXXXXXXXXX
RESET
The reset command resets all registers to Power-ON
Reset (POR) state. Refer to Table 15, page 18, for POR
Table 14. Reset Command
states or the paragraph entitled Power-ON Reset (POR) on
page 14 of this datasheet.
Reset 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 1 1 1 1 1 1 1XXXXXXXXXXXXXXXX
SPI COMMAND SUMMARY
Table 15 below provides a comprehensive list of SPI
commands recognized by the 33975 and the reset state of
each register. Table 16 and Table 17 contain the Serial
Output (SO) data for input voltages greater or less than the
Table 15. SPI Command Summary
MSB
Command Bits
threshold level. Open switches are always indicated with a
logic [0], closed switches are indicated with logic [1].
Setting Bits
LSBI
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Switch Status
Command
0 0 0 0 0 0 0 0XXXXXXXXXXXXXXXX
Settings Command
Bat=1, Gnd=0
0 0 0 0 0 0 0 1 X X X X X X X X SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
(Default state =
1)
Wake-Up/Interrupt Bit ₀
0
0
0
0
0
1
0
X
X
X
X
X
X
X
X SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
Wake-Up = 1
Nonwake-Up = 0
0 0 0 0 0 0 1 1 X X SG13 SG12 SG11 SG10 SG9 SG8 SG7 SG6 SG5 SG4 SG3 SG2 SG1 SG0
(Default state = 1)
Metallic Command
Metallic = 1
0 0 0 0 0 1 0 0 X X X X X X X X SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
Non-metallic = 0
0 0 0 0 0 1 0 1 X X SG13 SG12 SG11 SG10 SG9 SG8 SG7 SG6 SG5 SG4 SG3 SG2 SG1 SG0
(Default state =
1)
33975
18
Analog Integrated Circuit Device Data
Freescale Semiconductor