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X9418YS24 Datasheet(PDF) 3 Page - Xicor Inc. |
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X9418YS24 Datasheet(HTML) 3 Page - Xicor Inc. |
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3 / 21 page  X9418 Characteristics subject to change without notice. 3 of 21 REV 1.1.5 7/23/02 www.xicor.com PRINCIPLES OF OPERATION The X9418 is a highly integrated microcircuit incorporating two resistor arrays and their associated registers and counters and the serial interface logic providing direct communication between the host and the XDCP potentiometers. Serial Interface The X9418 supports a bidirectional bus oriented protocol. 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 provide the clock for both transmit and receive operations. Therefore, the X9418 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 X9418 are preceded by the start condition, which is a HIGH to LOW transition of SDA while SCL is HIGH (tHIGH). The X9418 continuously monitors the SDA and SCL lines for the start condition and will not respond to any command until this condition is met. Stop Condition All communications must be terminated by a stop condition, 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 during this period the receiver pulls the SDA line LOW to acknowledge that it successfully received the eight bits of data. The X9418 will respond with an acknowledge after recognition of a start condition and its slave address and once again after successful receipt of the command byte. If the command is followed by a data byte the X9418 will respond with a final acknowledge. Array Description The X9418 is comprised of two resistor arrays. 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 (VH/RH and VL/RL inputs). At both ends of each array and between each resistor segment is a CMOS switch connected to the wiper (VW/RW) output. Within each individual array only one switch may be turned on at a time. These switches are controlled by the 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. Device Addressing Following a start condition the master must output the address of the slave it is accessing. The most significant four bits of the slave address are the device type identifier (refer to Figure 1 below). For the X9418 this is fixed as 0101[B]. Figure 1. Slave Address The next four bits of the slave address are the device address. The physical device address is defined by the state of the A0–A3 inputs. The X9418 compares the serial data stream with the address input state; a successful compare of all four address bits is required for the X9418 to respond with an acknowledge. The A0–A3 inputs can be actively driven by CMOS input signals or tied to VCC or VSS. 1 00 A3 A2 A1 A0 Device Type Identifier Device Address 1 |
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