Specifications

Interrupt Controller (V40)
Interrupt Vectors
The CPU responds to all external interrupt requests by reading an
8-bit value from the interrupt device that indirectly points to the
subroutine used to service the device. The 8-bit value is called the
interrupt vector and the subroutine used to service the device is the
interrupt service routine.
The relationship between the interrupt vector provided by the ICU and
the address of the interrupt service routine is illustrated in Figure
8-12. The ICU provides a unique 8-bit vector for each interrupt input,
based on the IMKW value programmed. The CPU multiplies the
vector by four to point to the memory location that contains the
address of the service routine. The address of the interrupt service
routine includes the Instruction Pointer and Program Segment. The
application software must program the Instruction Pointer and
Program Segment into the appropriate memory locations before the
interrupt request is generated.
ICU CPU MEMORY
0
7
NMI
(N=2)
Programmed To
Provide Unique
Vector (N) For
Each Input
Multiplies Vector
(N) By Four
N
x4
4N
4N
4N+1
4N+2
4N+3
Offset
PFP (IP)
Segment
PS (CS)
Interrupt
Service
Routine
Figure 8–12. CPU Interrupt Vector Processing.
8-21