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CAUTION: The setting up of interrupt facilities beyon<
that of software sampling of the interrupt bit in th<
status byte requires knowledge of and experience ii
dealing with semiconductor components and circuitry. Ii
addition,, you should consult the Hardware volume of thi
System Technical Manual for the NCR DECISION MATE V.
I f you are using the 16-bit version of the processor for th<
NCR DECISION MATE V, you w ill require interrupt controllei
circ u itry, in addition to access to the interrupt lin e ol
the computer bus system.
The 8-bit processor (Z80A) has a characteristic which offen
a lim ited interrupt handling f a c ilit y with a minimum ol
hardware overhead, namely the Interrupt Mode 1. When thi!
interrupt mode is set (Instruction: IM 1 / Opcode; ED 56)
the setting of an interrupt (interrupt line goes low) force:
the transfer of program control to the hexadecimal address
38. The CP/M-80 operating system contains at this address ai
unconditional jump to the DDT u tility . This address is use<
when a breakpoint is encountered during the testing of «
program. I f use of the DDT is not required, i t is possibl«
to write a different jump instruction to address 38H. This
jump instruction can pass program control to your owi
interrupt service routine.
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