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Newer MacOS and OS X hardware come without a built in RS232 serial port but provide USB
Connect a serial DCC Adapter using a USB-to-Serial Adapter.
Macintosh serial ports used a "mini DIN-8" connector, which does not contain all of the signals of a typical RS232 connector. This page discusses how to wire an adapter so that a Macintosh can work with JMRI and a LocoBuffer or LocoBuffer II. The same adapter may also work with other protocols, particularly those that use "hardware flow control".
Note that the Macintosh has only one status output and input.
If the serial device uses "hardware flow control", it will assert the CTS lead to indicate when it's OK to send data. That has to be connected to the Macintosh input lead, or the program won't be able to send.
The status output will be set active by JMRI at startup. It should be connected to whatever status leads (e.g. RTS) the serial device looks at.
A good survey of (Macintosh) serial connections, including debugging techniques, is available at:
The information on this page was provided by Dick Bronson and Walter Thompson.