DS1867

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102199

DESCRIPTION

The DS1867 Dual Digital Potentiometer with EEPROM is the nonvolatile version of the popular DS1267

Dual Digital Potentiometer. The DS1867 consists of two digitally controlled potentiometers having 256-

position wiper settings. Wiper position is maintained in the absence of power through the use of

EEPROM memory cell arrays. Communication and control of the device are accomplished over a 3-wire

serial port which allows reads and writes of the wiper position. Both potentiometers can be stacked for

increased total resistance with the same resolution. For multiple-device, single-processor environments,

the DS1867 can be cascaded for control over a single 3-wire bus. The DS1867 is offered in three standard

resistance values.

OPERATION

The DS1867 contains two 256-position potentiometers whose wiper positions are set by an 8-bit value.

These two 8-bit values are written to a 17-bit I/O shift register which is used to store wiper position and

the stack select bit when the device is powered. An additional memory area, the shadow memory, stores

the 17-bit I/O shift register during a power-down sequence which provides for wiper nonvolatility. A

block diagram of the DS1867 is presented in Figure 1.

Communication and control of the DS1867 is accomplished through a 3-wire serial port interface that

CLK, and DQ.

active high input and is required to begin any communication to the DS1867. The CLK signal input is

used to provide timing synchronization for data input and output. The DQ signal line is used to transmit

potentiometer wiper settings and the stack select bit configuration to the 17-bit I/O shift register of the

DS1867.

state to a high state. Once the 3-wire port has been activated, data is latched into the part on the low to

high transition of the CLK signal input. Three-wire serial timing requirements are provided in the timing

diagrams of Figure 2(b) and (c).

Data written to the DS1867 over the 3-wire serial interface is stored in the 17-bit I/O shift register (see

Figure 3). The 17-bit I/O shift register contains both 8-bit potentiometer wiper position values and the

stack select bit. The composition of the I/O shift register is presented in Figure 3. Bit 0 of the I/O shift

register contains the stack select bit. This bit will be discussed in the section entitled Stacked

Configuration. Bits 1 through 8 of the I/O shift register contain the potentiometer-1 wiper position value.

Bit 1 will contain the MSB of the wiper setting for potentiometer-1 and bit 8 the LSB for the wiper

setting. Bits 9 through 16 of the I/O shift register contain the value of the potentiometer-0 wiper position

with the MSB for the wiper position occupying bit 9 and the LSB bit 16.