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processing, so that one or more End of Interrupt commands must
be sent to the 8259 Controller. Also, all I/O devices should be
reset in case an operation was underway at that time.
Interrupt Hex 1C - Timer Tick
This vector points to the code to be executed on every
system-clock tick. This vector is invoked while responding to the
timer interrupt, and control should be returned through an IRET
instruction. The power-on routines initialize this vector to point
to an IRET instruction, so that nothing will occur unless the
application modifies the pointer. It is the responsibility of the
application to save and restore all registers that will be modified.
Interrupt Hex 1D - Video Parameters
This vector points to a data region containing the parameters
required for the initialization of the 6845 on the video card. Note
that there are four 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 Hex 1E - Diskette Parameters
This vector points to a data region containing the parameters
required for the diskette drive. The power-on routines initialize
the 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
the other drives attached.
5-6
System BIOS
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- Section 1. System Board
- 64/256K System Board
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