This article describes sense codes and sense adapters and why they are used. Additional information can be found in article 15987: " Macintosh Monitor Sense Codes: Technical Description ".

Apple computers and video cards rely on sense codes in the display's video cable to determine what resolution at which to run. For example, an Apple 13-inch RGB monitor tells the Macintosh that it supports 640 x 480, so the Macintosh computer responds by displaying that resolution. When an Apple Multiple Scan Display is connected, it signals to the Macintosh that it can run in a range of resolutions. For example, a Multiple Scan 20 Display can support resolutions from 640 x 480 up to 1152 x 870. Sense Code technology is how Apple displays know what resolution to display.

Older Macintosh computers and Apple video cards do not have reprogrammable video drivers that allow them to switch to higher resolutions. If a Multiple Scan Display is connected to an older Macintosh or video card, it will be limited to 640 x 480 resolution.

Macintosh computers and video cards that fall into this class are:

• Video Cards - 4*8, 8*24, and 8*24GC
• LC , LC II, LC III (except 475, 476, and 630)
• Performa (except the 475, 476, and 630 family)
• PowerBook
• Duo Dock and MiniDock*
• Macintosh II family

* - The Duo Dock does not require a video adapter to change resolutions when System 7.5 is installed.

Sense Adapters

Sense code cable adapters allow older Macintosh and video cards to display higher resolutions on multiple scan displays. The adapters have a sense code for a higher resolution. This tricks the Macintosh into thinking it is hooked to a fixed frequency display like our 16-inch and 21-inch RGB displays.

The other solution, when using a multiple scan display, is to use a programmable display card like a Macintosh Display Card 24AC. Because this card is fully capable of recognizing the multiple scan sense codes and changing resolutions without restarting, even older Macintosh Systems work fine if they have a 24AC card.

Sense Code Adapter Specifications

832 by 624 Adapter - 16-inch Display

DB15M  DB15F  Pin Assignments

1       1     RED GND
2       2     RED VIDEO
3       3     C SYNC
5       5     GREEN VIDEO
6       6     GREEN GND
9       9     BLUE VIDEO
11     11     C & V SYNC GND
12     12     V SYNC
13     13     BLUE GND
14     14     H SYNC GND
15     15     H SYNC
SHELL  SHELL

Notes:
PINS 4 & 10 JUMPERED TOGETHER ON DB15 PLUG END.


1152 by 870  Adapter - 21-inch Display

DB15M    DB15F  Pin Assignments

1        1      RED GND
2        2      RED VIDEO
3        3      C SYNC
5        5      GREEN VIDEO
6        6      GREEN GND
9        9      BLUE VIDEO
12      12      V SYNC
13      13      BLUE GND
14      14      H SYNC GND
15      15      H SYNC
11      11      C & V SYNC GND
SHELL ð SHELL

Notes:
PINS 4,7,10,11 JUMPERED TOGETHER ON DB15 PLUG END.