The Macintosh II High-Resolution Video card is the replacement card for
Macintosh II Video card. One new feature with this card which may present a
problem is the automatic monitor sensing.
This feature, which has been incorporated into the video card for the Portrait
and Two-Page display, allows the video card to determine if a monitor is
attached to the card at boot time. This is accomplished by sensing either a
low (ground) or high (no connect) signal on the connector.
For DB-15 connectors, these sense lines are on pin 4, 7 and 10. The Macintosh
II High-Resolution Video card is a special case and only senses pin 4 of the
DB-15 connector.
In order for the card to work correctly with the monitors listed below, the
following is the minimum configuration of pins that must be connected:
Mac Mac
Hi-Res Hi-Res A II
Mono Pins RGB Pins RGB Pins
Pin Video Card Signal
1 Red video ground -> 1 1
2 Analog red video -> 2 2
3 TTL composite sync -> 3 3 3
4 Sense 0 -> 4 4
5 Analog grn video w/composite sync -> 5 5 5
6 Green video ground -> 6 6 6
7 Sense 1 (not used)
8 NC
9 Analog blue video -> 9 9
10 Sense 2 (not used)
11 Ground
12 Analog grn video w/composite sync
13 Blue video ground -> 13 13
14 Ground
15 NC
Shell Earth ground -> Shell Shell Shell
When Sense 0 (pin 4) is grounded, the card will generate a RS-343 video signal
compatible with the Macintosh High-Resolution Monochrome and High-Resolution
RGB monitor:
Horizontal Scanning = 35.000 KHz
Dot Clock = 30.24 MHz
Vertical Scanning = 66.67 Hz
When Sense 0 (pin 4) is not connected, the card will generate a RS-170 video
signal compatible with the Apple II AppleColor RGB monitor:
Horizontal Scanning = 15.734 Khz
Dot Clock = 12.27 Mhz
Vertical Scanning = 60.0 Hz
In addition, the frame buffer size is reduced to fit the display area of the
AppleColor RGB monitor.
(NOTE: This automatic sensing mechanism of the Apple High-Resolution Video card
is similar to the Apple Portrait and Two-Page display cards, but does not have
a shutdown mode -- that is, it does not show up in Control Panel -- when a
monitor is not attached.
This feature is useful when you have two video cards installed, but only use
one at a time. With the shutdown capability, the system software will
recognize only the card with a monitor attached. Thus if a card is assigned
the bootup monitor and the monitor is removed, the system will not send the
startup video to a non-existent monitor.)