PC33975AR2 datasheet(20/32 Pages) FREESCALE

20 / 32 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33975

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

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 10, shows the interaction

between changing input states and the INT and CS terminals.

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, 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 33975 device may be

disabled by programming the interrupt bits to logic [1 1 1].

Table 19 shows the programmable settings of the Interrupt

timer.

The scan timer sets the polling period between input

switch reads in Sleep mode. The period is set in the sleep

command and may be set to 000 (no period) to 111 (64 ms).

In Sleep mode when the scan timer expires, inputs will

behave as programmed prior to sleep command. The 33975

will wake up for approximately 125 µs and read the switch

inputs. At the end of the 125 µs, the input switch states are

compared with the switch state prior to sleep command.

When switch state changes are detected, an interrupt (when

enabled; refer to wake-up/interrupt command description on

page 15) is generated and the device enters Normal mode.

Without switch state changes, the 33975 will reset the scan

timer, inputs become tri-state, and the Sleep mode continues

until the scan timer expires again.

Table 20 shows the programmable settings of the Scan

timer.

Note The interrupt and scan timers are disabled in the

Normal mode.

Table 18. Sleep Command

Sleep Command

Command Bits

Table 19. Interrupt Timer

Bits 543

Interrupt Period

000

32 ms

001

64 ms

010

128 ms

011

256 ms

100

512 ms

101

1.024 s

110

2.048 s

111

No interrupt wake-up

Table 20. Scan Timer

Bits 210

Scan Period

000

No Scan

001

1.0 ms

010

2.0 ms

011

4.0 ms

100

8.0 ms

101

16 ms

110

32 ms

111

64 ms

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