Abstract: A circuit is described that allows four remote RS-232 transceivers to share a single UART. A dual four-to-one multiplexer permits transceiver IC1 to form a network with the four remote transceivers. RS-232 communications with one µC and more than one remote system can be problematic, because most µCs contain only one UART, which provides an interface between synchronous and asynchronous ports. The multiplexer in the figure below, IC2 , allows multiple channels (four, in this case) to share a single UART. The dual four-to-one multiplexer permits transceiver IC1 to form a network with the four remote transceivers IC3 to IC6. The table that follows defines the channel-selection codes. Selecting Channel 1, for instance, enables IC1 to communicate with IC3 without being loaded by IC4 to IC6. Pulldown resistors inside the remote transceivers force the outputs of unselected receivers to a known state. One UART and one multiplexer enable one RS-232 transceiver to communicate with four others. Channel Selection Codes Selected channel A1 A0 EN All channels disconnected X X 0 Channel 1 (IC3) 0 0 1 Channel 2 (IC4) 0 1 1 Channel 3 (IC5) 1 0 1 Channel 4 (IC6) 1 1 1 The circuit's supply-voltage range (3V to 5.5V) makes it compatible with 3V and 5V logic. IC2 receives its power directly from the V+ and V- terminals of IC1, whose ±5.5V outputs come from an internal charge pump. The multiplexer handles rail-to-rail signals, so obtaining its power from IC1 ensures that RS-232 signals pass directly through, regardless of amplitude. Each transceiver's charge pump requires four small capacitors (not shown), whose values depend on the VDD range but do not exceed 0.47µF. Note that pulling too much current from the charge-pump terminals of IC1, V+ and V-, can cause these rails to droop and can pull the IC's RS-232 transmission levels out of specification. A similar version of this article appeared in the September 28, 2000 issue of EDN. 의견을 보내주세요! 위 내용이 도움이 되셨나요? 여러분의 의견을 기다립니다 — Maxim은 보내주신 정정이나 제안사항을 반영하고 있습니다. 이 페이지를 평가하고 의견을 보내주십시오. 자동 업데이트 관심있는 분야의 애플리케이션 노트가 나올 때 자동으로 업데이트 받고 싶으세요? 그렇다면 EE-Mail™을 신청하십시오. 추가 정보   APP 588: Sep 18, 2002 MAX3221 1µA 전원 전류, AutoShutdown 기능을 가진 진정한 +3V ~ +5.5V RS-232 트랜시버 전체 데이터 시트 (PDF, 464kB) 무료 샘플 MAX399 정밀, 8채널/듀얼 4채널, 저전압, CMOS 아날로그 멀티플렉서 전체 데이터 시트 (PDF, 432kB) 무료 샘플   다운로드, PDF 형식 (31kB)  AN588, AN 588, APP588, Appnote588, Appnote 588