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Monitor Sense Codes

To identify the type of monitor connected, the computer first determines whether the adapter is connected. It does this by checking pin 11; on the new adapter, this pin is connected to the VSYNC signal. If the adapter is not found, the computer next checks to determine whether a DDC-type monitor is connected. DDC is the interface that provides monitor ID signals for VGA and SVGA monitors.

If the computer does not detect a DDC-capable monitor, it uses the Apple monitor sense codes on the signals MONID(0-2) in Table 3-4. Table 3-5 shows the sense codes and the extended sense codes for each of the monitors the card can support.

Note

The Apple Studio Display 17"/viewable 16" is listed in Table 3-5 with sense code value $06-23, but it is identified using DDC on most Macintosh computers.


Table 3-5 Monitor sense codes  

Monitor type

Standard
sense code

Extended sense code

(S2-0)

(S1,0)

(S2,0)

(S2,1)
Macintosh 21-inch Color Display 0 0 0 -- -- --
Macintosh Portrait Display 0 0 1 -- -- --
Macintosh 12-inch RGB Display 0 1 0 -- -- --
Apple Two-Page Monochrome Monitor 0 1 1 -- -- --
NTSC monitor 1 0 0 -- -- --
15-inch RGB monitor 1 0 1 -- -- --
Apple Multiple Scan 14 or 15 Display 1 1 0 0 0 0 0 1 1
Apple Multiple Scan 17 or 1705 Display 1 1 0 0 0 1 0 1 1
Apple Studio Display 17"/viewable 16" or Apple Multiple Scan 20 Display 1 1 0 1 0 0 0 1 1
Apple Studio Display 15", AppleStudio Display 21" with Colorsynch technology, AppleVision 850, 850av, 1710, and 1710av Displays, Macintosh 12-inch Monochrome Display, or AppleColor High Resolution RGB Monitor 1 1 0 1 0 1 0 1 1
PAL monitor 1 1 1 0 0 0 0 0 0
NTSC monitor, with convolution 1 1 1 0 1 0 1 0 0
VGA or SVGA monitor 1 1 1 0 1 0 1 1 1
Macintosh 16-inch Color Display 1 1 1 1 0 1 1 0 1
PAL monitor, with convolution 1 1 1 1 1 0 0 0 0
19-inch RGB monitor 1 1 1 1 1 1 0 1 0
No monitor connected 1 1 1 1 1 1 1 1 1

For a complete description of the sense code system, refer to Technote HW 30 Sense Lines. To find out how to obtain Apple Technical Notes, see Supplemental Reference Documents .

\xA9 1998 Apple Computer, Inc. — (Last Updated 5 Jan 99)

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