SECTION 6
Conversions and Interfaces
PEN*KEY
R
6200/6300 Hand-Held Computer Programmer’s Reference Guide 6-101
INT 15h, Function AH = 88h: Read Extended Memory Size
BIOS
Reads the amount of memory above 1 MB from the CMOS RAM locations 30h
and 31h.
On Entry:
AH = 88h
On Return:
If successful:
Carry = 0
AX = Number of contiguous 1 KB blocks of extended memory
If NOT successful:
Carry = 1
INT 15h, Function AH = 89h: Switch Processor to Protected Mode
BIOS
GDT describes the memory management environment in effect on return to the
calling program. All table descripters are initialized by the calling program
except the BIOS code segment descripter. The BIOS descripter access rights
byte is set to 9Bh. The address is set to F0000h and the segment limit is set to
0FFFFh. The DS, ES, and SS descripters are loaded with 0018h, 0020h and
0028h, respectively. The descripters built at these GDT offsets describe the
segments that these registers reference after the BIOS returns to the calling
program.
The program entering protected mode must construct its own IDT. This IDT
must not overlap the BIOS realĆmode table and must handle all interrupts while
the program is in protected mode.
On Entry:
AH = 89h
BH = Interrupt number for IRQ 0
BL = Interrupt number for IRQ 8
ES:SI = Pointer to GDT built by application
On Return:
If successful:
Carry = 0
AH = 00 (Successful move)
If NOT successful:
Carry = 1
AH = FFh (Unsuccessful move)
INT 15h, Function AX = 9002h: Pend On Key Press
4000API
BIOSĆinvoked to indicate pending until key is pressed.
On Entry:
AH = 90h
AL = 02h
On Return:
None
This interrupt is a PCĆlike system service.
"
NOTE:
INTERRUPT ROUTINES MUST NOT ISSUE THIS CALL.
6. Conversions and
Interfaces
