Multiplexer Enables Pseudomultidrop Rs-232 Transmission

Maxim Integrated Products, Inc.

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Keywords:
RS-232 /a> RS232 EIA/TIA-232, UART MUX, multiplexer, multi-drop RS-232 /a> shared UART RS232
Nov 01, 2000
APPLICATION NOTE 588
Multiplexer Enables Pseudomultidrop RS-232 /a> Transmission
Abstract: A circuit is described that allows four remote RS-232 /a> 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 /a> 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, IC
2
, allows multiple channels (four, in this case) to share a single UART The
dual four-to-one multiplexer permits Transceiver IC
1
to form a network with the four remote Transceivers IC
3
to
IC
6
. The table that follows defines the channel-selection codes. Selecting Channel 1, for instance, enables IC
1
to
communicate with IC
3
without being loaded by IC
4
to IC
6
. 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 /a> Transceiver to communicate with four others.