DS1809

101999

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A continuous pulse input (“push and hold”) is defined as lasting longer that ½ second. A continuous pulse

input will cause the wiper position to move one position every 100 milliseconds following the initial ½-

second hold time. The total time to transcend the entire potentiometer given a continuous pulse input is

provided by the equation:

½(second) + 62 X 100 ms = 6.7 (seconds)

If the wiper position of the DS1809 is incremented to an end-position, it will stay at that position until the

device receives an opposite direction input pulse command over the UC or DC inputs. For example, if the

terminal.

The UC and DC control inputs are designed to support simple pushbutton inputs or CPU generated

inputs. Figure 2 illustrates the requirements for pushbutton generated controls. For manual pushbutton

controls all that is required are the desired pushbuttons to implement contact closure. No external

debounce or timing circuitry is needed to support the pushbutton operation.

Applications using CPU generated controls must power the UC and DC control pins in a high state to

avoid any inadvertent wiper position movement. To help prevent inadvertent wiper position movement

during a power-up, the DS1809 locks out the control port inputs for a minimum time of 10 ms.

WIPER STORAGE

As stated earlier, the DS1809 provides for two methods of nonvolatile wiper storage using internal

EEPROM memory cells. These two methods include an autostore configuration and a command initiated

storage operation, both of which utilize the STR input pin. The EEPROM cell array of the DS1809 is

designed to accept greater than 50k writes.

Autostorage

The autostore configuration is designed to provide wiper position storage as the part powers down;

writing the current wiper position into memory. The configuration for initiating the automatic storage

capability of the DS1809 is shown in Figure 3. As shown in this configuration, two external devices are

required to insure proper wiper storage. This includes a Schottky diode and a 10-uf capacitor. The

automatic store configuration will cause the DS1809 to initiate storage of wiper position when power

power for wiper storage.

Command-Initiated Wiper Storage

The DS1809 will also support a command-initiated wiper storage operation during powered conditions.

For command initiated storage the STR pin should be held in a low state on power-up; otherwise the part

will assume an autostore configuration. As shown in Figure 5, a low-to-high pulse lasting at least 1

µs on

the STR input will cause the DS1809 to initiate the storage of the current wiper position into EEPROM