DEMO MANUAL DC1786A LTC2871IUHF RS232/RS485 Multiprotocol Transceiver with Integrated Termination DESCRIPTION block for convenient connection of a transmission line. Demonstration circuit 1786A showcases the LTC2871 Because the LTC2871 contains half-/full-duplex switching RS232/RS485 multiprotocol transceiver with integrated control it is unnecessary to jumper A and B to Y and Z for termination. Separate supply inputs power the interface half-duplex operation. and logic sections, permitting operation of the logic con- trol and I/O down to 1.7V. LEDs indicate when supplies Design files for this circuit board are available at are present. All control pins are accessible via a turret DEMO MANUAL DC1786A QUICK START PROCEDURE In summary, DC1786A features a turret for each and every Jumpers LTC2871 logic, interface and supply pin. In addition the Jumper blocks are included to set the state of each control supply pins have banana jacks, and the control pins are pin to V or GND. If the shorting jumper is set in the EXT L connected to jumper blocks to establish their states. position, the control pin is connected to its associated turret and external signalling may be applied. Failure Components to select one of the three positions results in a floating Components on DC1495A are divided into four basic control pin. The turret is disconnected and there are no groups: internal or on-board pull-ups to establish the logic state if the jumper block is open. R1-R9: 100 resistors included in series with the control signal turrets to limit fault current arising from any ac- As shipped, jumpers on DC1786A are set to enable all cidental misconnections of the turrets or jumpers. transmitters and receivers, with RS485 set to full duplex with terminations enabled. D1, D2, R11, R15: V and V supply indicator LEDs and CC L current limiting resistors. See the data sheet Pin Functions and Function tables for a complete description of the control pin functions. A brief R12, R13, R14: 10k pull-ups to V on DI and DIN1, DIN2. L summary is given here: C1-C5, L1: supply generation and bypassing components JP1, LB: Loopback Enable. A logic high loops driver input for the LTC2871 (U1). signals immediately back to associated receiver outputs. Loopback is interrupted when a receiver is disabled. Default LTC2871 Operation position low, loopback disabled. The LTC2871 contains two RS232 drivers, two RS232 JP2, H/F: RS485 Half-Duplex Select Input. A logic low receivers, one RS485 driver and one RS485 receiver. selects full-duplex operation where the RS485 receiver The input(s) and output(s) of each of these elements is responds to signals on the A and B pins. A logic high separately available and can be interconnected with other selects half-duplex operation where the RS485 receiver elements without conflict between abs max ratings or responds to signals on the Y and Z pins. Default position loading in the disabled state. low, full duplex enabled. The RS485 transceiver includes a special half-/full-duplex JP3, TE485: RS485 Termination Enable. A logic high switching feature. In full-duplex mode, the receiver inputs enables 120 terminations across A-B and Y-Z. Default are connected to the A and B pins, while the driver is position high, RS485 terminations enabled. connected to Y and Z. In half-duplex mode, the receiver inputs are moved to Y and Z so that there is no need to JP4, CH2: RS232 Channel 2 Disable. A logic high disables jumper A-B to Y-Z when switching between half- and RS232 driver 2 and receiver 2, independent of RX232 and full-duplex modes. DX232. Default position low, RS232 CH2 enabled. Lastly, RS485 terminations are included in the LTC2871. JP5, RX485: RS485 Receiver Enable. A logic low enables The terminations can be engaged or disengaged as con- the RS485 receiver. Default position low, RS485 receiver trolled by a termination enable control line, TE485. enabled. dc1786af 2