19-5047 4/15 DS2480B Serial to 1-Wire Line Driver BENEFITS AND FEATURES PIN ASSIGNMENT Simplifies the Design of a Low-Cost, Universal GND 1 8 RXD RS-232 COM Port to 1-Wire Interface True-Ground 1-W 2 7 TXD o Interface to an RS-232 COM Port for Reading and Writing 1-Wire Devices NC 3 6 POL o Works with Bipolar as well as Unipolar Logic 4 5 Signals VDD VPP o Slew Rate Controlled 1-Wire Pulldown and 8-Pin SO (150 mil) Active Pullup to Accommodate Long Lines and Reduce Radiation o Communicates at Data Rates of 9.6kbps PIN DESCRIPTION (default), 19.2kbps, 57.6kbps, and 115.2kbps GND - Ground o Self-Calibrating Time Base with 5% 1-W - 1-Wire Input/Output Tolerance for Serial and 1-Wire NC - No Connection Communication V - 4.5V to 5.5V DD o User-Selectable RXD/TXD Polarity V - Optional EPROM Minimizes Component Count When PP Programming Voltage Interfacing to 5V Based RS232 Systems or Directly to UARTs POL - RXD/TXD Polarity Select o Smart Protocol Combines Data and Control TXD - Serial Data from UART Information Without Requiring Extra Pins RXD - Serial Data to UART o Compatible with Optical, IR, and RF to RS232 Converters Single Product Supports Various iButton or ORDERING INFORMATION 1-Wire Device Types for Easy System Integration TEMP PIN- o Supports Reading and Writing at Standard PART RANGE PACKAGE and Overdrive Speeds DS2480B+ -40C to +85C 8 SO o Provides Strong Pullup to 5V for Temperature DS2480B+T&R -40C to +85C 8 SO and EEPROM 1-Wire Devices + Denotes a lead(Pb)-free/RoHS-compliant package. o Programs 1-Wire EPROM Devices with T&R = Tape and reel. External 12V Power Supply o Programmable 1-Wire Timing and Driver Characteristics Accommodate a Wide Range 1-Wire and iButton are registered trademarks of of Slave Device Configurations at Standard Maxim Integrated Products, Inc. Speed o Operates Over 4.5V to 5.5V from -40C to +85C DESCRIPTION The DS2480B is a serial port to 1-Wire interface chip that supports standard and overdrive speeds. It con- nects directly to UARTs and 5V RS232 systems. Interfacing to RS232C (12V levels) requires a passive clamping circuit and one 5V to 12V level translator. Internal timers relieve the host of the burden of generating the time-critical 1-Wire communication waveforms. In contrast to the DS9097(E) where a full character must be sent by the host for each 1-Wire time slot, the DS2480B can translate each character Maxim Integrated 1 DS2480B into eight 1-Wire time slots, thereby increasing the data throughput significantly. In addition, the DS2480B can be set to communicate at four different data rates, including 115.2kbps, 57.6kbps, and 19.2kbps, with 9.6kbps being the power-on default. Command codes received from the hosts crystal controlled UART serve as a reference to continuously calibrate the on-chip timing generator. The DS2480B uses a unique protocol that merges data and control information without requiring control pins. This approach maintains compatibility to off-the-shelf serial to wireless converters, allowing easy realization of 1-Wire media jumpers. The various control functions of the DS2480B are optimized for 1- Wire networks and support the special needs of all current 1-Wire devices including EPROM-based add- only memories, EEPROM devices, and 1-Wire thermometers. See Application Note 192: Using the DS2480B Serial 1-Wire Driver for detailed software examples. DETAILED PIN DESCRIPTION PIN SYMBOL DESCRIPTION 1 GND Ground Pin. Common ground reference and ground return for 1-Wire bus 1-Wire Input/Output Pin. 1-Wire bus with slew-rate-controlled pulldown, active pullup, ability to switch in V to program EPROM, and ability to switch PP 2 1-W in V through a low-impedance path to program EEPROM, or perform a DD temperature conversion. 3 N.C. No Connection Power Input Pin. Power supply for the chip and 1-Wire pullup voltage, 5V 4 V 10%, must always be lower than or equal to V . V should be derived from DD PP DD V by a separate voltage regulator whenever possible. PP EPROM Programming Voltage. 12V supply input for EPROM programming. 5 V If EPROM programming is not required, connect this pin directly to the systems PP 5V supply. RXD/TXD Polarity Select. RXD/TXD polarity select tied to GND for RS232 6 POL (12V or 5V) connection tied to V for direct connection to UART chip. DD Serial Data from UART. Data input from host (inverted or true) maximum 7 TXD voltage swing -0.3V to V + 0.3V for logic thresholds see DC specifications. DD Serial Data to UART. Signal output to host push-pull driver with CMOS 8 RXD compatible levels for true 12V RS232 systems an external level translator must be provided. OVERVIEW The DS2480B directly interfaces a 5V serial communication port with its lines TXD (transmit) and RXD (receive) to a 1-Wire bus. In addition the device performs a speed conversion allowing the data rate at the communication port to be different from the 1-Wire data rate. Several parameters relating to the 1-Wire port and its timing as well as the communication speed at both the port and the 1-Wire bus are configurable. The circuit to achieve these functions is outlined in the block diagram (see Figure 1). The device gets its input data from the serial communication port of the host computer through pin TXD. For compatibility with active-high as well as active-low systems, the incoming signal can be inverted by means of the polarity input POL. The polarity chosen by hard-wiring the logic level of this pin is also valid for the output pin RXD. If for minimizing the interface hardware an asymmetry between RXD and TXD is desired, this can be achieved by setting the most significant bit of the speed control parameter to a 1 (see Configuration Parameter Value Codes). With the MS bit of the speed control set to 1, the polarity at TXD is still selected by the logic level at POL, but the polarity at RXD will be the opposite of what the logic level at POL specifies. Maxim Integrated ............................................................................................................................................................................................. 2