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DS1668 Datasheet(PDF) 4 Page - Dallas Semiconductor |
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DS1668 Datasheet(HTML) 4 Page - Dallas Semiconductor |
4 / 10 page DS1668, DS1669, DS1669S 081895 4/10 Dallastats interpret input pulse widths as the means of controlling wiper movement. A single pulse width input over the UC, DC, or D terminals will cause the wiper position to move 1/64th of the total resistance. All inputs, UC, DC, or D, are inactive when in the high state. A transition from a high to low on these inputs is consid- ered the beginning of pulse activity. A single pulse is defined as being greater than 1 ms but lasting no longer than a second when using the contact closure inputs UC and DC. When using the D input a single pulse is defined as being greater than 1 µs but lasting no longer than 1 second. This is shown in Fig- ures 4a and 6a. Repetitive pulsed inputs can be used to step through each resistive position of the device (see Figures 4a and 6b). The requirement for repetitive pulsed inputs is that pulses must be separated by a minimum time of 1 ms. If not, the Dallastat will interpret repetitive pulses as a single continuous pulse. Pulse inputs lasting longer than 1 second will cause the wiper to move one position every 100 ms following the initial 1 second hold time. The total time to transcend the entire potentiometer using a continuous input pulse is given in the equation below: 1 (second) + 63 X 100 ms = 7.3 (seconds) In single pushbutton mode or when using the digital source input, as the wiper reaches the end of the poten- tiometer its direction of movement reverses. This will occur whether or not the input is a continuous pulse or a sequence of repetitive pulses. Changing the direction of wiper movement in single pushbutton mode or digital source mode is also accomplished by a period of inac- tivity on the UC or D inputs for (minimum) 1 second or greater. In dual pushbutton mode, the direction is con- trolled by the UC and DC inputs. No wait states are required to change wiper direction in dual pushbutton mode. Additionally, in dual pushbutton mode as the wiper reaches the end of the potentiometer, the direc- tion of wiper movement will not change. Wiper position will remain at the potentiometers’ end until an opposite direction input is given. All control inputs, UC, DC, and D, are internally pulled up with a 100K ohm resistance. Additionally, the UC and DC inputs are internally debounced and require no external components for input signal conditioning. The DS1668/DS1669 are provided with two supply inputs –V and +V. The maximum voltage difference between the two supply inputs is + 8.0 volts while the minimum voltage difference is +4.5 volts. All input levels are referenced to the negative supply input, –V. The volt- age applied to any Dallastat terminal must not exceed the negative supply voltage (–V ) by –0.5 or the positive sup- ply voltage (+V) by + 0.5 volts. The minimum logic high level must be +2.4 volts with reference to the –V supply voltage input. A logic low level with reference to the –V supply voltage has a maximum value of +0.8 volts. Dal- lastats exhibit a typical wiper resistance of 400 ohms with a maximum wiper resistance of 1000 ohms. The maxi- mum wiper current allowed through the Dallastat is speci- fied at 1 milliamps (see DC Electrical Characteristics). NONVOLATILE WIPER SETTINGS Dallastats maintain the position of the wiper in the absence of power. This feature is provided through the use of EEPROM type memory cell arrays. During nor- mal operation the position of the wiper is determined by the input multiplexer. Periodically, the multiplexer will update the EEPROM memory cells. The manner in which an update occurs has been optimized for reliabil- ity, durability, and performance. Additionally, the update operation is totally transparent to the user. When power is applied to the Dallastat, the wiper setting will be the last recorded in the EEPROM memory cells. If the Dallastat setting is changed after power is applied, the new value will be stored after a delay of 2 seconds. The initial storage of a new value after power–up, occurs when the first change is made, regardless of when this change is made. After the initial change on power–up, subsequent changes in the Dallastat EEPROM memory cells will occur only if the wiper position of the part is moved greater than 12.5% of the total resistance range. Any wiper movement after initial power–up which is less than 12.5% will not be recorded in the EEPROM memory cells. Since the Dallastat contains a 64–to–1 multiplexer, a change of greater than 12.5% corre- sponds to a change of the fourth LSB. Changes or storage to the EEPROM memory cells must allow for a 2 second delay to guarantee that updates will occur. The EEPROM memory cells are specified to accept greater than 80,000 writes before a wear–out condition. If the EEPROM memory cells do reach a wear–out condition, the Dallastat will still function prop- erly while power is applied. However, on power–up the device’s wiper position will be that of the position last recorded before memory cell wear out. |
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