Re: [Gumstix-users] Serial RS232 -> Null Modem

[Dave H. <dhy...@gm...>]

HI Bruce,

> If you wonder where that "silly" gummstix connector came from, which
> *really* only uses three wires out of eight (i.e., TX, RX and GND), it is
> from an Apple Macintosh.  See for example:
>
>    http://www.epanorama.net/documents/lan/mac_serial.html
>
> Maybe you can find one of those "locally"?

While the Mac uses the same Mini-DIN-8 connector, the pinout used by
the Mac is different (but compatible if you only use TxD and RxD). It
uses differentially encoded RS-422, while the gumstix is using RS-232.

Here's a pinout of the RS-422 connector used by the Mac:
http://pinouts.ru/SerialPorts/MacRs422_pinout.shtml

Here's a pinout of the SGI RS-232 pinout used by the gumstix:
http://pinouts.ru/SerialPorts/sgi8_pinout.shtml

So, a Mac null-modem cable would work for simple Tx/Rx/Gnd, but won't
work properly for the flow control signals.

Mac Mini-DIN-8 to Mac Mini-DIN-8 cables actually wire through all 8 signals.

Mac Mini-DIN-8 to DB-9 Null modem cables normally connect the HSKi and
HSKo signals through to the CTS/RTS signals. Notice that the HSKi and
HSKo aren't on the same pins as CTS and RTS for the SGI pinout.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/