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PIC24 question about #ROM and embedding data.
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Ttelmah



Joined: 11 Mar 2010
Posts: 19195

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PostPosted: Wed Dec 04, 2019 9:14 am     Reply with quote

Yes, it is quite 'interesting'...
I've used processors with 8bit, 11bit, 12bit, 14bit, 16bit, 24bit, 32bit & 64bit
instruction words, so realising that you have to adjust what you are thinking
to the hardware, has become 'second nature'. It is complicated by 'standards',
like using Intel Hex' to transfer data for programming, since the need to
align this, and that the internal data size is 16bit, so if transferring to/from
instruction memory the only way that a lossless alignment can be done is
to use 32bits to transfer each 24bits, does make it quite confusing.
This is further complicated by PSV, which maps part of the program memory
into the RAM address space (allowing you to actually have RAM pointers to
the ROM space), but which does this by only using the low 16bits of
each instruction in the mapping.
Fun all the way... Very Happy

This is also further complicated by the Harvard architecture, since here the
actual data paths for the ROM space are 24bits wide. While with a
conventional processor the data path widths for ROM and RAM are always
the same.
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