The Macintosh LC supports 3 different timing modes:
- Macintosh 12-inch RGB Display's 512x384
- Macintosh 12-inch RGB Display's 560x384 (generated by Apple IIe card,
- Macintosh 12-inch Monochrome Display, Macintosh High-Resolution
Monochrome, Macintosh High-Resolution RGB (640x480)
In 640x480 mode, Macintosh LC uses the CPU clock (31.3344 MHz) as the
pixel clock. This is opposed to the 30.24 MHz clock that is normally
specified. This results in 32 extra pixels per scan line. The 640 active
pixels are centered in the active video field with 16 black pixels placed
on either side. Horizontal and vertical scan rates remain the same. A
visual distortion from square pixels will occur, making the pixels 3% too
narrow. The Macintosh 12-inch Monochrome display will be able to correct
for this distortion, but the current monochrome and RGB monitors will not.
The 560x384x4 Apple IIe mode is selectable only when an Apple IIe card is
present. The card is necessary because the 17.234 MHz oscillator required
for this video mode is located on the Apple IIe card itself.