DS1844 Quad Digital Potentiometer www.maxim-ic.com FEATURES PIN ASSIGNMENT Four independent, digitally controlled 64- PS 1 20 V CC position potentiometers H2 2 19 H1 Two interface control options H3 3 18 H0 - 5-wire serial - 2-wire addressable W3 4 17 W0 Standard resistance values L3 5 16 L0 - DS1844-010 10 k L2 6 15 L1 - DS1844-050 50 k W2 7 14 W1 - DS1844-100 100 k R/W, A0 8 13 SCL, CLK Mixed resistor value combinations (contact A2, RST 9 12 SDA, D IN factory for availability) GND 10 11 A1, D OUT Operating Temperature Range - Industrial: -40C to +85C 20-Pin DIP (300-mil) Device D20-Pin SeOscription IC (300-m il) 20-Pin TSSOP (173-mil) PIN DESCRIPTION V - 2.7V to 5.5V CC PS - Port Select A0, A1, A2 - Device Select Pins (2-Wire) SDA - Serial Data I/O (2-Wire) SCL - Serial Clock (2-Wire) R/ W - Read/Write enable (5-Wire) RST - Serial Port Reset Input (5-Wire) D - Serial Port Data Input (5-Wire) IN CLK - Serial Port Clock Input (5-Wire) D - Cascade Data Output (5-Wire) OUT H -H - High-end Terminal of Pot 0 3 L -L - Low-end Terminal of Pot 0 3 W -W - Wiper Terminal of Pot 0 3 GND - Ground DESCRIPTION The DS1844 Quad Digital Potentiometer is a four-channel, digitally controlled linear potentiometer. Each potentiometer is comprised of 63 equi-resistive sections and has three terminals accessible to the user. These include the high side terminals, H , the wiper terminals, W , and the low-side terminals, L The X X X. wiper position on the resistor ladder is selected via an 8-bit register value. Communication and control of the device are supported by two types of serial interface. These include a 5-wire I/O shift register interface and a 2-wire addressable interface. 1 of 14 053105 DS1844 The DS1844 is available in standard 10 k , 50 k , and 100 k versions. Mixed resistor combinations are also available through custom setups. The DS1844 is specified to operate over the industrial temperature range: -40 C to +85 C. Packages for the DS1844 include 20-pin DIPs, SOICs, and TSSOPs. OPERATION The DS1844 contains four 64-position potentiometers. Each potentiometer is independent and has three accessible terminals, which include H , L , and W . Each potentiometer is comprised of 63 individual X X X resistor elements. Between each resistor element is a tap-point that is multiplexed to the wiper terminal, W . Additionally, the wiper terminal can be multiplexed directly to the end-terminals, H and L . X X X The DS1844 supports two interface control options. Both options allow for the direct placement of the wiper position on the resistor ladder. Each wiper has an associated 6-bit register used to hold its positional value. The DS1844 is a volatile device and will always power-up with the wiper positions set to mid-tap (position 32-decimal). The end-terminal H will have wiper position value 63-decimal and the L terminal X X will have wiper position value 0-decimal. Because the DS1844 is a 64-position device only 6 bits of data are necessary to write a wipers value. However, communication with the DS1844 will require using a full 8 bits, with the remaining 2 bits specifying the potentiometer selected. A discussion of proper communication protocol is provided under the section entitled Serial Port Operation. A block diagram of the DS1844 is shown in Figure 1. SERIAL PORT OPERATION As stated, the DS1844 can support two types of serial interface control. This includes a 5-wire serial interface and a 2-wire addressable interface. The type interface supported during operation is selectable via the port select input pin, PS. Additionally, certain pins provide dual functionality dependent on the serial port selected. The pin description table lists pin functionality according to the interface selected. 5-Wire Serial Port Control The 5-wire serial interface provides an 8-bit I/O shift register for loading and reading wiper data. The 5- wire serial interface control is selected when the port select input, PS, is in a low state. This interface is controlled by the signals RST , DIN, DOUT, CLK, and R/ W . Timing diagrams for the 5-wire serial port can be found in Figure 3. Timing information for the 5-wire serial port is provided in the AC Electrical Characteristics table for 5-wire serial communications. Data is loaded MSB first and in multiples of 8 bits. The 8-bit data to specify wiper position has the format or protocol as that shown in Figure 2. The 8-bit data is divided into potentiometer select data and wiper position value. The 6 least significant bits of data specify the wiper position value while the 2 most significant bits specify the potentiometer to be loaded. This allows the interface control logic/protocol to provide order independent potentiometer loading, as well as variable-length data loads. As stated earlier, the 5-wire serial port is selected when the PS input is in a low state. If the device will only be used in the 5-wire mode, the PS input can be tied directly to ground. Communication via the 5- wire interface is enabled when RST is in a high state. A low-to-high transition on the RST indicates the start of a communication transaction with the DS1844. While RST is high, data can be read or written to the part. Data will be read or written dependent on the state of the read-write enable input, R/ W . The state of R/ W must be stable before a low-to-high transition on RST . Once the RST input has begun a communication transaction, the serial port will ignore any transitions on the R/ W input. 2 of 14