] Actually, assembling from and to an external mapper should be faster, if
] Compass itself is located in the internal mapper, since reading the source
] and writing the result doesn't undo the blocks selection.
]
When the R800 accesses external memory, either for read or for write, the
S1990 slows the whole stuff down. The S1990 makes sure that the timing of the
signals on the external bus is compliant with the MSX specifications. That
is, both the read and the write cycle will take 3 cycles on the 3.58MHz
clock. Which is 6 cycles for the R800. Compare that to the 2 cycles (worst
case scenario) for accessing the internal memory and you have your delay
explained.
By the way, the 1-cycle fast access mode of the R800 is only used when memory
is accessed to fetch instructions. When accessing memory for other purposes,
e.g. to push something to the stack or read a byte from memory, both the row
and column address will be set-up.
Kind regards,
Alex Wulms
--
Alex Wulms/XelaSoft - MSX of anders NIX - Linux 4 ever
See my homepage for info on the *** XSA *** format
http://www.inter.nl.net/users/A.P.Wulms
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