Vertical Interrupt Feature - IBM RT Series Hardware Reference Manual

handle the additional character rows on the screen. The assembly
language required for both an alphanumeric and a graphics screen
is shown below.
moval,7
intlO
movax,1112
mov bl,O
intlO
movax,1200
move bl,20
intlO
int3
movax,f
intlO
movax,1123
mov bl,O
mov dl,2B
intlO
movax,1200
mov bl,20
intlO
int3
;Monochrome alphanumeric mode
; video interrupt call
;character generator BIOS routine
;load 8 by 8 double dot character font
; video interrupt call
;alternate screen routine
;select alternate print screen routine
;video interrupt call
;Monochrome graphic mode
;video interrupt call
;character generator BIOS routine
;load 8 by 8 double dot character font
;43 character rows
; video interrupt call
;alternate screen routine
;alternate print screen routine
;video interrupt call
Vertical Interrupt Feature
The Enhanced Graphics Adapter can be programmed to create an
interrupt each time the vertical display refresh time has ended.
An interrupt handler routine must be written by the application to
take advantage of this feature. The CRT Vertical interrupt is on
IRQ2. The CPU can poll the Enhanced Graphics Adapter Input
Status Register 0 (bit 7) to determine whether the CRTC caused
the interrupt to occur.
The Vertical Retrace End Register (11 H) in the CRT controller
contains two bits which are used to control the interrupt circuitry.
The remaining bits must be output as per the value in the mode
table.
72 IBM Enhanced Graphics Adapter