COP8SG-EPU National Semiconductor, COP8SG-EPU Datasheet - Page 34

• Manufacturer Part Number: COP8SG-EPU
• Description: BOARD PROTOTYPE/TARGET COP8
• Manufacturer: National Semiconductor
• Type: MCUr

Specifications of COP8SG-EPU

• Contents: *
• For Use With/related Products: Cop 8
• For Use With: COP8SG-EPU - BOARD PROTOTYPE/TARGET COP8
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Interrupts
VIS Execution
When the VIS instruction is executed it activates the arbitra-
tion logic. The arbitration logic generates an even number
between E0 and FE (E0, E2, E4, E6 etc...) depending on
which active interrupt has the highest arbitration ranking at
the time of the 1st cycle of VIS is executed. For example, if
the software trap interrupt is active, FE is generated. If the
external interrupt is active and the software trap interrupt is
not, then FA is generated and so forth. If the only active inter-
rupt is software trap, than E0 is generated. This number re-
places the lower byte of the PC. The upper byte of the PC re-
mains unchanged. The new PC is therefore pointing to the
vector of the active interrupt with the highest arbitration rank-
(Continued)
FIGURE 17. VIS Operation
34
ing. This vector is read from program memory and placed
into the PC which is now pointed to the 1st instruction of the
service routine of the active interrupt with the highest arbitra-
tion ranking.
Figure 17 illustrates the different steps performed by the VIS
instruction. Figure 18 shows a flowchart for the VIS instruc-
tion.
The non-maskable interrupt pending flag is cleared by the
RPND (Reset Non-Maskable Pending Bit) instruction (under
certain conditions) and upon RESET.
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