03 September 2013, 02:40 | #1 |
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32-bit access on 16-bit bus?
When you do a long write on a 16-bit bus, what are the rules for which part (upper or lower word) are written first?
Question stands for all 680x0. (This in relation to chip register writes.) |
03 September 2013, 11:14 | #2 |
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http://en.wikipedia.org/wiki/Endiann...s_and_hardware
"The Motorola 6800 and 68k series of processors use the big-endian format, and for this reason, the big-endian format is also known as the Motorola convention. Other well-known processors that use the big-endian format include the Xilinx Microblaze, SuperH, IBM POWER, and System/360 and its successors such as System/370, ESA/390, and z/Architecture. The PDP-10 also used big-endian addressing for byte-oriented instructions." http://en.wikipedia.org/wiki/Endiann...mory_locations |
03 September 2013, 12:02 | #3 |
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The answer to my question is either "upper then lower" or "lower then upper".
Endianness does not come into the equation as far as I can see? |
03 September 2013, 12:08 | #4 |
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AFAIK 68020+ always writes upper word first. 68000/010 has some exceptions, for example CLR.L <memory>, MOVE x,-(An).
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03 September 2013, 13:14 | #5 |
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03 September 2013, 15:39 | #6 |
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03 September 2013, 18:31 | #7 |
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Hmmm i think that article in Wikipedia describe order of operation for 32 bit on 16 bit bus but perhaps i misunderstood your question.
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04 September 2013, 00:46 | #8 |
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