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Shield used to connect a microcontroller to a full duplex RS-422 serial line (RX and TX pairs) and a half duplex management line (DTR pair) through CAT5 cable.
To connect a RPUno on a multidrop serial line.
The transceivers have fail-safe biasing (e.g. the logic state is defined above -50mV) so they can be disabled when the UART TX is high and all receivers will see a high. Sparkfun has an RS485 shield that does this for a single pair. When RS-422 has an automatic enable it is controlled like RS-232 (almost), e.g. the core control software for the UART does not need to know about the transceivers (since they are not enabled by the core). The only concern is to make sure multiple devices don't answer at the same time. A big deal for myself is that avrdude can upload firmware when I configure a point to point mode.
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United States Postal Service: Priority Mail
Priority Mail Small Flat Rate Box will hold two RPUno, or two shields (RPUftdi or RPUadpt) and an RPUno.
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I am working on what may be thought of as a garden SCADA system, it is based on securely connecting a host computer through RS-422 to multiple microcontrollers. I have strayed from RS-485 in favor of retaining existing software (e.g. avrdude, picocom, PySerial...) and have an interface that can act like an interactive terminal session.