The ISL81334 and ISL41334 are two-port interface ICs in which each port can be independently configured as a single RS-485, RS-422 transceiver, or as a dual (2 Tx, 2 Rx) RS-232 transceiver. With both ports set to the same mode, two RS-485, RS-422 transceivers, or four RS-232 transceivers are available. If either port is in RS-232 mode, the onboard charge pump generates RS-232 compliant ±5V Tx output levels from a single VCC supply as low as 4.5V. Four small 0.1µF capacitors are required for the charge pump. The transceivers are RS-232 compliant, with the Rx inputs handling up to ±25V, and the Tx outputs handling ±12V. In RS-485 mode, the transceivers support both the RS-485 and RS-422 differential communication standards. The receivers feature “full fail-safe” operation, so the Rx outputs remain in a high state if the inputs are open or shorted together. The transmitters support up to three data rates, two of which are slew rate limited for problem-free communications. The charge pump disables when both ports are in RS-485 mode, thereby saving power, minimizing noise, and eliminating the charge pump capacitors. Both RS-232 and RS-485 modes feature loopback and shutdown functions. Loopback internally connects the Tx outputs to the corresponding Rx input, to facilitate board level self-test implementation. The outputs remain connected to the loads during loopback, so connection problems (such as shorted connectors or cables) can be detected. Shutdown mode disables the Tx and Rx outputs, disables the charge pumps, and places the IC in a low current (µA) mode. The ISL41334 is a QFN packaged device that includes two additional user-selectable, lower speed and edge rate options for EMI-sensitive designs, or to allow longer bus lengths. It also features a logic supply pin (VL) that sets the VOH level of logic outputs, and the switching points of logic inputs, to be compatible with another supply voltage in mixed voltage systems. The QFN also adds active low Rx enable pins to increase design flexibility, allowing Tx/Rx direction control, through a single signal per port, by connecting the corresponding DE and RXEN pins together. For a single port version of these devices, please see the ISL81387, ISL41387 datasheet.


  • ±15kV (HBM) ESD protected bus pins (RS-232 or RS-485)
  • Two independent ports, each user selectable for RS-232 (2 transceivers) or RS-485, RS-422 (1 transceiver)
  • Single 5V (10% tolerance) supply
  • Flow-through pinouts simplify board layouts
  • Pb-Free (RoHS compliant)
  • Large (2.7V) differential VOUT for improved noise immunity in RS-485, RS-422 networks
  • Full fail-safe (open/short) Rx in RS-485, RS-422 mode
  • Loopback mode facilitates board self-test functions
  • User-selectable RS-485 data rates (ISL41334 only); Fast speed 20Mbps, Slew rate limited 460kbps, Slew rate limited 115kbps
  • Fast RS-232 data rate up to 650kbps
  • Low current Shutdown mode 42µA
  • QFN package saves board space (ISL41334 only)
  • Logic supply pin (VL) eases operation in mixed supply systems (ISL41334 only)



  • Gaming applications (such as slot machines)
  • Single board computers
  • Factory automation
  • Security networks
  • Industrial/Process control networks
  • Level translators
  • Such as RS-232 to RS-422
  • Point of sale (POS) equipment
  • Dual channel RS-485 interfaces


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