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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 4554
Maxim > Design Support > Technical Documents > Application Notes > Communications Circuits > APP 4554
Maxim > Design Support > Technical Documents > Application Notes > Interface Circuits > APP 4554
Keywords: RS-485 adapter, full duplex, point-to-multipoint half duplex, voltage monitors
APPLICATION NOTE 4554
RS-485 Adapter Converts Data Lines from Full- to
Half-Duplex
By: Massimo Caprioli
Jan 06, 2011
Abstract: An adapter circuit consisting of an RS-485 transceiver (MAX3076 or MAX13086) and a voltage
monitor used as a timer (MAX641X) allows an existing point-to-point full duplex circuit to function in a
more-complex point-to-multipoint half-duplex system.
A similar version of this article appeared in the June 21, 2007 issue of Electronic Design magazine.
Multiprotocol interface ICs (such as the MAX3162 from Maxim) can be used to connect a UART to an
RS-485 bus architecture called point-to-point full-duplex (PTP-FD). The PTP connection usually requires
that drivers and receivers be kept constantly enabled, and therefore "present" on the line. When such a
circuit board must fit into a point-to-multipoint half-duplex system (PTM-HD), the entire board (usually)
must be redesigned (Figure 1).
Figure 1. The adapter circuitry indicated by "?" lets you incorporate existing PTP-FD communication
links into an existing PMP-HD system.
A simple trick, however, can adapt an existing PTP-FD board (providing a single link between two
terminals) for use in the more complex PTM-HD architecture (one master and multiple slaves, connected
by multiple links), thereby preserving and making reusable the hardware already designed and
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