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Download ADSP-219x/2191 DSP Hardware Reference
Transcript
DAG Operations Pre-modify addressing does not change (or update) the I register. The other type of modified addressing is post-modify addressing. In post-modify addressing, the DAG outputs the I register value unchanged, then the DAG adds an M register or immediate value, updating the I register value. Figure 4-3 on page 4-10 compares pre- and post-modify addressing. PRE-MO DIFY NO I R EGISTER UPDATE S Y NTAX : PM(Ix+Mx) DM(Ix+Mx) POST-MODIFY I REG ISTER UPDA TE S Y NTA X : PM(Ix+=Mx) DM(Ix+=Mx) 2. U P DAT E I OU TP UT 1. OUT PUT I + + M M I+ M I+M Figure 4-3. Pre-Modify and Post-Modify Operations The difference between pre-modify and post-modify instructions in the DSP’s assembly syntax is the operator that appears between the index and modify registers in the instruction. If the operator between the I and M registers is += (plus-equals), the instruction is a post-modify operation. If the operator between the I and M registers is + (plus), the instruction is a 4-10 ADSP-219x/2191 DSP Hardware Reference
