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Getting 422 in and out of Your SGI

By Chris Pirazzi.

You will need a serial port that talks RS-422 (that spec is now officially called TIA/EIA-422-B).

SGI serial ports talk one of three electrical protocols:

• All SGI machines have at least one RS-232 (officially, EIA/TIA-232-E) port. So you can always use a 232 to 422 converter. We strongly recommend self-powered converters rather than converters which suck power off the 232 port's flow control or data lines. Currently, SGI does not officially support any particular converter. An officially SGI-supported solution to this, which will produce a spec 422 signal, is in the works. Unofficially, we have had some luck on O2s with the port-powered B&B 422LP9R adapter at short (10ft) distances with unterminated cables. Customers have also reported luck with the Antona 6090 adapter for Mac MIDI interfaces on O2; that adapter may also work for 422 deck control. If you have had good or bad experiences with particular adapters, send us some mail and we'll include your experience here.

• Some SGI serial ports talk 422 directly, and you're set.

• Some SGI serial ports talk Macintosh levels. Although a Macintosh port consists of a differential RX pair and a differential TX pair like 422, the line drivers and receivers on these ports will detect and transmit the voltage levels in Apple's "Guide to the Macintosh Family Hardware," not TIA/EIA-422-B (and also not TIA/EIA-423-A, as some have asserted). Plus, TIA/EIA-422-B defines only RX-, RX+, TX-, TX+, and GND. The Macintosh spec defines three additional signals: HSKi, HSKo, and GPi. The Macintosh level SGI ports were designed to accept Macintosh LocalTalk devices and Macintosh Serial devices such as MIDI interfaces. Some customers have reported luck using these ports to drive 422 decks at short (10ft) distances with unterminated cables. Your mileage may vary.

When the serial port people saw how many pixel packings there were, (see The Pixel Rosetta Stone: Packings and Colorspaces), they got jealous. In case you're trying to roll your own conversion cables or converters, we will tell you the pinouts of all 232, 422, and Macintosh ports on all SGI machines we know about, and where we got the information from. When you see a pin with no function in the tables below, it means the pin is reserved and you must not connect it to anything.

Onyx and Challenge machines have built-in female DB9s with this 232 pinout (source: man serial(7)):

Pin	232 Function
1
2	TD
3	RD
4	RTS
5	CTS
6
7	GND
8	DCD
9	DTR

Onyx and Challenge machines have built-in female DB9s with this 422 pinout (source: man serial(7)):

Pin	422 Function
1
2	TX-
3	RX-
4
5
6	GND
7	TX+
8	RX+
9

On Onyx and Challenge machines, you can get the Audio Serial Option (ASO). ASO boards have six female DB9s with the same pinout as the built-in Onyx/Challenge 232 ports (source: man asoser(7)). You can switch these ports to 422 mode, where they have this 422 pinout (source: man asoser(7)):

Pin	422 Function
1	TX+
2	TX-
3	RX-
4
5
6	RX+
7	GND
8
9

The Octane, Onyx2, and Origin 2000's male DB9 ports have this IBM PC 232 pinout (source: man serial(7) on IRIX 6.4):

Pin	232 Function
1	DCD
2	RD
3	TD
4	DTR
5	GND
6
7	RTS
8	CTS
9

You can switch the Octane, Onyx2, and Origin 2000's male DB9 serial ports into Macintosh mode using code we will show later in this section. When you do this, their Macintosh pinout is (source: man serial(7) on IRIX 6.4):

Pin	Macintosh Function
1
2	RX-
3	TX-
4	TX+
5	GND
6	RX+
7	HSKo (defined by Apple)
8	HSKi (defined by Apple)
9

Not to be outdone, the Origin 200's male DB9 serial port has a different Macintosh pinout (yes, this is a bug, it is miswired. source: upcoming SGI audio FAQ item):

Pin	Macintosh Function
1
2	RX-
3	TX-
4
5	GND
6	RX+
7	TX+
8	HSKi (defined by Apple)
9

This O200 miswiring only applies to Macintosh mode. O200 serial ports behave like O2000 and Octane for 232 mode.

The female Mini-DIN-8 connector on Indigo, Indy, and Indigo2 has this 232 pinout (source: man serial(7) on IRIX 6.4):

Pin	232 Function
1	DTR
2	CTS
3	TD
4	GND
5	RD
6	RTS
7	DCD
8	GND

You can switch the Indy and Indigo2 systems into Macintosh mode using code we will show later. The Macintosh pinout of the female Mini-DIN-8 on these machines is (source: man serial(7) on IRIX 6.4):

Pin	Macintosh Function
1	HSKo (defined by Apple)
2	HSKi (defined by Apple)
3	TX-
4	GND
5	RX-
6	TX+
7	GPi (defined by Apple)
8	RX+

The O2's male DB9 serial ports have the same IBM PC 232 pinout as Octane, Onyx2, and Origin. The O2's ports do not do 422 or Macintosh levels; you need a converter (source: man serial(7) on IRIX 6.4).