AT89C5122D-RDRUM datasheet(182/208 Pages) ATMEL

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182

AT83R5122, AT8xC5122/23

4202F–SCR–07/2008

Exiting from Power-down

Mode

The microcontroller will exit from Power-down or Idle modes upon a reset or INT1 inter-

rupt which is a multiplexing of the interruptions generated by the CPRES pin (Card

detection), RxD flag (UART reception) and INT1 pin.

Keyboard Interface

The keyboard interface applies only to AT8xC5122 version.

Entering in Power-down Mode

In order to reduce the power consumption, the microcontroller can be set in power-down

or idle mode by software (see Table 13, PCON register). Before activating these modes

the application will need to configure the keyboard interface as follows:

•

Set all keyboard’s ouputs pins KB Rx at low level by writing a 0 on the ports. This

operation has a double effect:

–

any key that is pressed generates an interrupt capable of waking-up the

microcontroller,

–

Set all bits KBE.x in KBE registers to enable interrupts.

Exiting from Power-down

Mode

The microcontroller will exit from Power-down Mode upon a reset or any interrupt gener-

ated by a key press. Note that 1024 clocks are necessary to exit from power-down mode

when a keyboard interrupt occurs. This means that there will be a delay between the

time at which the key is pressed and the time at which the application is able to identify

the key.

Watchdog Timer during

Power-down and Idle

Mode

In Power-down mode the oscillator stops, which means the WDT also stops. While in

Power-down mode the user does not need to service the WDT. There are 2 methods of

exiting Power-down mode : by a hardware reset or by a level activated external interrupt

which is enabled prior to entering power-down mode. When Power-down is exited with

hardware reset, servicing the WDT should occur as it normally does whenever

AT8xC5122D is reset. Exiting Power-down with an interrupt is significantly different. The

interrupt is held low long enough for the oscillator to stabilize. When the interrupt is

brought high, the interrupt is serviced. To prevent the WDT from resetting the device

while the interrupt pin is held low, the WDT is not started until the interrupt is pulled high.

It is suggested that the WDT be reset during the interrupt service for the interrupt used

to exit Power-down.

To ensure that the WDT does not overflow within a few states of exiting of powerdown, it

is best to reset the WDT just before entering powerdown.

In the Idle mode, the oscillator continues to run. To prevent the WDT from resetting

while the microcontroller is in Idle mode, the user should always set up a timer that will

periodically exit Idle, service the WDT, and re-enter Idle mode.

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