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Maxim > Design Support > Technical Documents > Application Notes > Analog Switches and Multiplexers > APP 588
Maxim > Design Support > Technical Documents > Application Notes > Interface Circuits > APP 588
Keywords: RS-232, rs232, EIA/TIA-232, UART, MUX, multiplexer, multi-drop RS-232, shared UART,
RS232, transceivers
APPLICATION NOTE 588
Multiplexer Enables Pseudomultidrop RS-232
Transmission
Sep 18, 2002
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, 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.
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