INT 0x10 - 0x05 - Select Active Display Page

Request/Call:

reg	value	descr
AH	0x05
AL	parm	new page number (see Video Pages)

for PCjr only:

reg	value	descr
AL	0x80	read CRT/CPU page registers
	0x81	set CPU page register BL: CPU page register
	0x82	set CRT page register BH: CRT page register
	0x83	set bot CRT and CPU page register BL: CPU page register BH: CRT page register

the CPU page determines which 16K block of the first 128K of physical memory will be mapped at B800h by the hardware
the CRT page determines the start address of the memory used by the video controller

reg	descr
BH	CRT page register
BL	CPU page register

returns data from BIOS DATA AREA locations 40:50, 40:60 and 40:61
the 6845 can also be used to read the cursor position
the return data can be circumvented by direct port I/O to the 6845 CRT Controller since this function returns the data found in the BIOS Data Area without actually checking the controller
to determine whether the requested page actually exists, use AH=0Fh to query the current page after making this call