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X9C303S8I Datasheet(PDF) 3 Page - Intersil Corporation |
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X9C303S8I Datasheet(HTML) 3 Page - Intersil Corporation |
3 / 10 page 3 FN8223.0 March 11, 2005 PRINCIPLES OF OPERATION There are three sections of the X9C303: the input con- trol, counter and decode section; the nonvolatile mem- ory; and the resistor array. The input control section operates just like an up/down counter. The output of this counter is decoded to turn on a single electronic switch connecting a point on the resistor array to the wiper output. Under the proper conditions the contents of the counter can be stored in nonvolatile memory and retained for future use. The resistor array is com- prised of 99 individual resistors connected in series. At either end of the array and between each resistor is an electronic switch that transfers the potential at that point to the wiper. The wiper, when at either fixed terminal, acts like its mechanical equivalent and does not move beyond the last position. That is, the counter does not wrap around when clocked to either extreme. The electronic switches on the device operate in a “make before break” mode when the wiper changes tap positions. If the wiper is moved several positions, multiple taps are connected to the wiper for tIW (INC to VW change). The RTOTAL value for the device can temporarily be reduced by a significant amount if the wiper is moved several positions. When the device is powered-down, the last counter position stored will be maintained in the nonvolatile memory. When power is restored, the contents of the memory are recalled and the counter is reset to the value last stored. Instructions and Programming The INC, U/D and CS inputs control the movement of the wiper along the resistor array. With CS set LOW the device is selected and enabled to respond to the U/D and INC inputs. HIGH to LOW transitions on INC will increment or decrement (depending on the state of the U/D input) a seven-bit counter. The output of this counter is decoded to select one of one-hundred wiper positions along the resistive array. The value of the counter is stored in nonvolatile mem- ory whenever CS transitions HIGH while the INC input is also HIGH. The system may select the X9C303, move the wiper, and deselect the device without having to store the lat- est wiper position in nonvolatile memory. The wiper movement is performed as described above; once the new position is reached, the system would the keep INC LOW while taking CS HIGH. The new wiper posi- tion would be maintained until changed by the system or until a power-down/up cycle recalled the previously stored data. This would allow the system to always power-up to a preset value stored in nonvolatile memory; then during system operation minor adjustments could be made. The adjustments might be based on user preference: system parameter changes due to temperature drift, etc... The state of U/D may be changed while CS remains LOW. This allows the host system to enable the device and then move the wiper up and down until the proper trim is attained. MODE SELECTION SYMBOL TABLE CS INC U/D Mode L H Wiper Up L L Wiper Down H X Store Wiper Position H X X Standby Current L X No Store, Return to Standby WAVEFORM INPUTS OUTPUTS Must be steady Will be steady May change from Low to High Will change from Low to High May change from High to Low Will change from High to Low Don’t Care: Changes Allowed Changing: State Not Known N/A Center Line is High Impedance X9C303 |
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