CHAPTER 5 CPU SOFTWARE ARCHITECTURE
Figure 5.2-1 Example of Using XCHW A, PC
[Main routine] ... MOVW A, #PUTSUB XCHW A, PC
DB 'PUT OUT DATA', EOL
MOVW A, #1234H
...
[Subroutine] |
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PUTSUB XCHW A, EP |
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PUSHW A |
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PTS1 MOV A, @EP |
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INCW EP |
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MOV IO, A | ... Output table data here. |
CMP A, #EOL |
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BNE PTS1 |
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POPW A |
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XCHW A, EP |
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JMP @A |
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■CALLV #k
This instruction is used for branching to a subroutine address registered in the table. In this addressing mode, the information about #k is included in the instruction code and the tale addresses listed in Table 5.2- 1 are created. After saving the contents of the current program counter (PC) in the stack, the program branches to the address in the table. Because it is a
Table 5.2-1 Jump Address Table
#k | Address table (upper jump address : lower jump address) |
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0 | FFC0H:FFC1H |
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1 | FFC2H:FFC3H |
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2 | FFC4H:FFC5H |
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3 | FFC6H:FFC7H |
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4 | FFC8H:FFC9H |
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5 | FFCAH:FFCBH |
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6 | FFCCH:FFCDH |
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7 | FFCEH:FFCFH |
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