Name: Nokia 616
Brand: Nokia
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Nokia Customer Care TF4 Technical Information

Company Confidential TFE-4/RV-1

Company Confidential

Figure 11: Write Cycle to Flash

Power saving signal (PS).

In order to reduce the power consumption on the bus a Power Save function is intro-

duced. This function reduces the amount of switching on the external bus. Power is con-

sumed in a digital system when a signal changes state. The power is consumed when the

capacitive load is either charged or discharged. The capacitive load is introduced by the

interconnection itself and of cause by the input at the receiving device. Internally in dig-

ital circuits the capacitive load is lower, than at the interconnect level at the printed cir-

cuit board. Therefore it is an advantage if the amount of changes on the external

interconnection, i.e. between two digital circuits, can be minimized. Therefore on a wide

bus like an address/data bus in a microprocessor system, power is saved, if the data to be

transmitted on the external bus, causes a minimum amount of transitions. This can be

achieved by comparing the previously data on the bus, with the data to be transmitted,

and if inverting the data to be transmitted causes less transitions to be performed on the

external bus, the data is inverted, before it is output on the data bus. To inform that the

data is inverted, a control signal is used to inform the receiving device, that the data

must be inverted before any further processing. Data on the address/data bus is bit wise

compared which means that the data previously on D0 (D0e) is compared with the new

data to be output on D0 (D0i). If the two data elements are the same (D0e=D0i) a logic

“0” is indicated to the comparing device. If the two data elements are not the same

(D0e=NOT(D0i)) a logic “1” is indicated to the comparing device. If there are more equal

signal than unequal signals on the address/data bus, the new data is not inverted before

it is sent out on the bus. If there are more unequal than equal data on the address/data

bus, the data is inverted before it is sent out on the bus. The status whether the data that

is presented on the address/data bus is inverted or not, is indicated by a separate signal

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