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X9438WS24I Datasheet(PDF) 3 Page - Intersil Corporation |
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X9438WS24I Datasheet(HTML) 3 Page - Intersil Corporation |
3 / 18 page 3 FN8199.0 March 11, 2005 PRINCIPLES OF OPERATION The X9438 is an integrated microcircuit incorporating two resistor arrays, two operational amplifiers and their associated registers and counters; and the serial interface logic providing direct communication between the host and the digitally controlled potenti- ometers and operational amplifiers. Serial Interface The X9438 supports a bidirectional bus oriented proto- col. The protocol defines any device that sends data onto the bus as a transmitter and the receiving device as the receiver. The device controlling the transfer is a master and the device being controlled is the slave. The master will always initiate data transfers and pro- vide the clock for both transmit and receive operations. Therefore, the X9438 will be considered a slave device in all applications. Clock and Data Conventions Data states on the SDA line can change only during SCL LOW periods (tLOW). SDA state changes during SCL HIGH are reserved for indicating start and stop conditions. Start Condition All commands to the X9438 are preceded by the start condition, which is a HIGH to LOW transition of SDA while SCL is HIGH (tHIGH). The X9438 continuously monitors the SDA and SCL lines for the start condition and will not respond to any command until this condi- tion is met. Stop Condition All communications must be terminated by a stop con- dition, which is a LOW to HIGH transition of SDA while SCL is HIGH. Acknowledge Acknowledge is a software convention used to provide a positive handshake between the master and slave devices on the bus to indicate the successful receipt of data. The transmitting device, either the master or the slave, will release the SDA bus after transmitting eight bits. The master generates a ninth clock cycle and dur- ing this period the receiver pulls the SDA line LOW to acknowledge that it successfully received the eight bits of data. The X9438 will respond with an acknowledge after recognition of a start condition and its slave address and once again after successful receipt of the com- mand byte. If the command is followed by a data byte the X9438 will respond with a final acknowledge. Operational Amplifier The voltage operational amplifiers are CMOS rail-to- rail output general purpose amplifiers. They are designed to operate from dual (±) power supplies. The amplifiers may be configured like any standard ampli- fier. All pins are externally available to allow connec- tions with the potentiometers or as stand alone amplifiers. Potentiometer/Array Description The X9438 is comprised of two resistor arrays and two operational amplifiers. Each array contains 63 discrete resistive segments that are connected in series. The physical ends of each array are equivalent to the fixed terminals of a mechanical potentiometer (RH and RL inputs). At both ends of each array and between each resistor segment is a CMOS switch connected to the wiper (RW) output. Within each individual array only one switch may be turned on at a time. These switches are controlled by a volatile wiper counter register (WCR). The six bits of the WCR are decoded to select, and enable, one of sixty-four switches. The WCR may be written directly, or it can be changed by transferring the contents of one of four associated data registers into the WCR. These data registers and the WCR can be read and written by the host system. INSTRUCTIONS AND PROGRAMMING Device Addressing Following a start condition the master must output the address of the slave it is accessing. The most signifi- cant four bits of the slave address are the device type identifier (refer to Figure 1). For the X9438 this is fixed as 0101[B]. Figure 1. Address/Identification Byte Format 1 00 A3 A2 A1 A0 Device Type Identifier Device Address 1 X9438 |
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