Commodore 128 Programmer's Reference Manual page 602

592 COMMODORE 128
0
LATCH ENABLE
BIT BIT
IRST ERST
IMDC EMDC
IMMC EMMC
ILP ELP
IRQ
WHEN SET
Actual raster count = stored raster count (bit 0)
MOB-DATA collision (first bit only) (bit 1)
MOB-MOB collision (first bit only) (bit 2)
First negative transition of LP per frame (bit 3)
When IRQ/ output low (bit 7)
Table 16-14. Interrupt Register Definitions
I!
To enable an interrupt request to set the IRQ/ output to 0, the corresponding interrupt
enable bit in register 53274 ($D01A) must be set to "1". Once an interrupt latch has
been set, the latch may be cleared only by writing a "1" to the associated bit in the
interrupt register. This feature allows selective handling of video interrupts without
software storing the active interrupts.
SCREEN BLANKING
The display screen can be blanked by clearing the BLNK bit (bit 4) in register 53265
($D011) to zero (0). When the screen is blanked, the entire screen displays the exterior
color specified by register 53280 ($D020). When blanking is enabled, only transparent
(phase 1) memory accesses are required, permitting fiill processor utilization of the
system bus. However, sprite data will be accessed if the sprites are not also disabled.
U
DISPLAY ROW/COLUMN SELECT
The normal display screen consists of 25 rows of 40 character regions per row. For
special display purposes, the display window is reduced to 24 rows of 38 characters.
There is no change in the format of the display information, except that characters (bits)
adjacent to the exterior border area are covered by the border.