C511 datasheet(98/128 Pages) SIEMENS

98 / 128 page

Power Saving Mode

Semiconductor Group

8-2

8.1

Idle Mode

In the idle mode the oscillator of the C511/513 continues to run, but the CPU is gated off from the

clock signal. However, the interrupt system, the serial port, and all timers are further provided with

the clock. The CPU status is preserved in its entirety: the stack pointer, program counter, program

status word, accumulator, and all other registers maintain their data during idle mode.

The reduction of power consumption, which can be achieved by this feature depends on the number

of peripherals running.

If all timers are stopped and the serial interface is not running, the maximum power reduction can

be achieved. This state is also the test condition for the idle mode

CC.

So the user has to take care which peripheral should continue to run and which has to be stopped

during idle mode. Also the state of all port pins – either the pins controlled by their latches or

controlled by their secondary functions – depends on the status of the controller when entering idle

mode.

Normally the port pins hold the logical state they had at the time idle mode was activated. If some

pins are programmed to serve their alternate functions they still continue to drive the output during

idle mode if the assigned function is on. This applies also to the serial interface in case it cannot

finish reception or transmission during normal operation. The control signals ALE and PSEN are

held at logic high levels.

Table 8-1

Status of External Pins During Idle and Power-Down Mode

Outputs

Last Instruction Executed from

Internal Code Memory

Last Instruction Executed from

External Code Memory

Idle

Power-Down

Idle

Power-Down

ALE

High

Low

High

Low

PSEN

High

Low

High

Low

Port 0

Data

Address

Float

Port 1

Data/alternate

outputs

Data/alternate

outputs

Data/alternate

outputs

Data/alternate

outputs

Port 2

Data

Address

Data

Port 3

Data/alternate

outputs

Data/last output

Data/alternate

outputs

Data/last output

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