Other Read/Write Memory Usage - IBM AT 5170 Technical Reference

separate tables, and all four must be reproduced if all modes of
operation are to be supported. The power-on routines initialize
this vector to point to the parameters contained in the ROM video
routines.
Interrupt IE-Diskette Parameters:
This vector points to a
~
data region containing the parameters required for the diskette
drive. The power-on routines initialize this vector to point to the
parameters contained in the ROM diskette routine. These default
parameters represent the specified values for any IBM drives
attached to the system. Changing this parameter block may be
necessary to reflect the specifications of other drives attached.
Interrupt IF-Graphics Character Extensions:
When
operating in graphics modes 320 x 200 or 640 x 200, the
read/write character interface will form a character from the
ASCII code point, using a set of dot patterns. ROM contains the
dot patterns for the first 128 code points. For access to the
second 128 code points, this vector must be established to point
at a table of up to lK, where each code point is represented by 8
bytes of graphic information. At power-on time, this vector is
initialized to 000:0, and the user must change this vector if the
additional code points are required.
~
Interrupt 40-Reserved:
When a Fixed Disk and Diskette Drive
Adapter is installed, the BIOS routines use interrupt 40 to
revector the diskette pointer.
Interrupt 41 and 46-Fixed Disk Parameters:
These vectors
point to the parameters for the fixed disk drives, 41 for the first
drive and 46 for the second. The power-on routines initialize the
vectors to point to the appropriate parameters in the ROM disk
routine if CMOS is valid. The drive type codes in CMOS are
used to select which parameter set the vector points to. Changing
this parameter hook may be necessary to reflect the specifications
of other fixed drives attached.
Other Read/Write Memory Usage
The IBM BIOS routines use 256 bytes of memory from absolute
hex 400 to hex 4 FF. Locations hex 400 to 407 contain the base
5-8 System BIOS