SAB80515 Datasheet, PDF (100/270 Pages) Siemens Semiconductor Group – 8-Bit Single-Chip Microcontroller Family

On-Chip Peripheral Components
7.6.2 Power Saving Modes of the SAB 80515/80535
Dlfferences between the Power-Down Modes of the SAB 80C515/80C535 and the SAB 80515/
80535
The power-down mode of the SAB 80515/80535 allows retention of 40 bytes on-chip RAM through
a backup supply connected to the V_PD pin.
The ACMOS versions SAB 80C515/80C535 have the following additional features:
– The same power supply (pin V_CC) for active, power-down (retention of the whole int. RAM
area), and idle mode.
– An extra pin (PE) that allows enabling/disabling of the power-saving modes.
– A software protection that enables the power saving modes via special function register
PCON (Power Control Register).
Hardware Enable for the Use of the Power Saving Modes
To provide power saving modes together with effective protection against unintentional entering of
these modes, the SAB 80C515/80C535 has an extra pin for disabling the use of the power saving
modes. This pin is called PE (power saving enable), and its function is as follows:
PE = 1 (logic high level): Use of the power saving modes is not possible. The instruction
sequences used for entering these modes will not affect the
normal operation of the device.
PE = 0 (logic low level): All power saving modes can be activated as described in the following
sections.
When left unconnected, the pin PE is pulled to high level by a weak internal pullup. This is done to
provide system protection by default.
In addition to the hardware enable/disable of the power saving modes, a double-instruction
sequence which is described in the corresponding sections is necessary to enter power-down and
idle mode. The combination of all these safety precautions provides a maximum of system
protection.
Application Example for Switching Pin PE
For most applications in noisy environments, certain components external to the chip are used to
give warning of a power failure or a turn off of the power supply.
These circuits could be used to control the PE pin. The possible steps to go into power-down mode
could then be as follows:
– A power-fail signal forces the controller to go into a high priority interrupt routine. This interrupt
routine saves the actual program status. At the same time pin PE is pulled low by the power-
fail signal.
– Finally the controller enters power-down mode by executing the relevant double-instruction
sequence.
Semiconductor Group
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