3.15.3 MAC Write-Back
The Write-Back ability of the MAC class of DSP
instructions facilitates efficient processing of algorithms. This feature allows one
mathematical operation to be performed with one accumulator and the rounded contents of the
other accumulator to be stored in the same cycle.
The following addressing modes are supported:
- W0, W1, W2, W3, W13 or W14 register direct: the rounded contents of the non-target accumulator are written into the destination register as a 1.15 (Word mode) or 1.31 (Long Word mode) fraction. As is the case for any register direct word write, the value written is zero extended to 32-bits prior to being written into the destination WREG.
- [W13++] or [W15++] register indirect with post increment: the rounded contents of the non-target accumulator are written into the address pointed to by W13 or W15 as a 1.15 (Word mode) or 1.31 (Long Word mode) fraction. The destination EA W-reg is then incremented by two (for a word write) or four (for a long word write).