DS1809
3 of 9
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
wiper position is incremented to the R
H
terminal using the UC input control, it will stay at that position
until UC is first deactivated, and then the DC input is activated to move the wiper position towards the R
L
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
(V
CC
) to the device is removed. The 10-uF capacitor and Schottky diode are used to provide supplemental
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 s on
the STR input will cause the DS1809 to initiate the storage of the current wiper position into EEPROM
when V
CC
is present.
