DEMO MANUAL DC1851A LTC2872 Dual Multiprotocol Transceiver with Integrated Termination DESCRIPTION Demonstration circuit 1851A showcases the LTC 2872 available at a terminal block for convenient connection of RS232/RS485 dual multiprotocol transceiver with inte- a transmission line. Because the LTC2872 contains half-/ grated termination. Separate supply inputs power the full-duplex switching, it is unnecessary to jumper A and interface and logic sections, permitting operation of the B to Y and Z for half-duplex operation. logic control and I/O down to 1.7V. LEDs indicate when Design files for this circuit board are available at supplies are present. Control pins are accessible via tur- DEMO MANUAL DC1851A QUICK START PROCEDURE Overview In summary, DC1851A features a turret for each and every LTC2872 logic, interface and supply pin. In addition the The LTC2872 dual multiprotocol transceiver contains two supply pins have banana jacks, and the control pins are identical channels, each comprising two RS232 drivers, connected to jumper blocks to establish their states. two RS232 receivers, and one RS485 driver and receiver. The two channels are largely independent, sharing only Components loopback and duplex control and a split supply generator. Components on DC1851A are divided into four basic Operating power is derived from the V input, while a CC groups: separate logic I/O supply pin (V ) permits the LTC2872 L to adapt to any logic level ranging from 1.7V up to V . CC R1-R11: 100 resistors included in series with the con- trol signal turrets to limit fault current arising from any Another key feature is that RS232 and RS485 inputs and accidental misadventures with the turrets or jumpers. outputs may be interconnected without regard to loading or voltage limitations. Allowing that only one interface D1, D2, R16, R17: V and V supply indicator LEDs CC L type is enabled at any given moment, input and output and current limiting resistors. characteristics of the selected standard are preserved R12-R15: 10k pull-ups to V on DY1, DZ1, DY2 and L without violating the limits of the disabled sections. The DZ2. LTC2872 also includes selectable RS485 terminations, as well as switching for half- and full-duplex modes, permit- C1-C5, L1: supply generation and bypassing compo- ting full digital control and eliminating the need for external nents for the LTC2872 (U1). jumpers or relays to change between modes. LTC2872 Operation DC1851A includes: Each channel of the LTC2872 contains two RS232 drivers, Bananas and turrets for supply connections along the two RS232 receivers, one RS485 driver and one RS485 upper edge of the board. receiver. The 485/232 control lines enable either the RS485 Green LEDs to indicate the presence of V and V . Note or RS232 elements for each channel. CC L that the V LED, D1, unavoidably dims and extinguishes L The RS485 transceiver includes a special half-/full-duplex at V < 2V. L switching feature. In full-duplex mode, the receiver inputs Turrets for logic I/O along the left edge of the board. are connected to the A and B pins, while the driver is connected to Y and Z. In half-duplex mode, the receiver Turrets for RS232 and RS485 interface connections inputs are moved to Y and Z so that there is no need to along the right edge of the board. jumper A-B and Y-Z when switching between half- and Terminal blocks J5 and J6 for RS485 connections. full-duplex modes. Turrets and jumpers for selecting modes along bot- RS485 terminations are included in the LTC2872. The tom edge of board. There are no pull-up or pull-down terminations are controlled by a termination enable control resistors on the control lines known states must be line, TE485. asserted by jumpers or by applying a definitive logic level to the turrets. 10k pull-up resistors on driver inputs DY1, DZ1, DY2 and DZ2. They assert a known logic-1 state when these turrets are left open circuit. dc1851af 2