] At 10:55 PM 8/20/98 +0300, you wrote:
]
] >And we should make sure that the protocol is smart enough to handle 'slow'
] >(compared to the cpu speed) changing lines. When the line is somewhere
] >between low and high for a too long time, you can get flipping 0/1 levels
] >because of noice. Flipping long enough for the CPU to notice it...
]
] Is there really a voltage level that is exactly between 0 and 1?
]
] I can imagine a system like this that would have far less problems:
] 0V means "0"
] 5V means "1"
] When the level goes from 0V to 5V, at 3V the bit flips to "1".
] When the level goes from 5V to 0V, at 2V the bit flips to "0".
]
] Does anyone know how things work in the MSX ICs?
As far as I know, digital circuits work with treshold values. Something like:
4-5V = high
0-2V = low
And 2-4V is undefined. Due to electronic noise in the circuitry, one moment
it will be considerd low. And the other moment it will be considered high.
So, yes, you can get flipping 0/1 levels. That is one of the reasons why most
computersystems do have a clock. Just to give the circuits time to stabilize.
A few nano to a few milli seconds after the change of the clockpuls
(depending on the type of circuitry used, line length and other things),
everything will be stable again. The 4-5V level or the 0-2V level will have
been reached. And from that moment on you can safely read your bus again.
Please correct me if I'm wrong. I'm no expert on this subject but it is
something which I vaguely remember from years ago.
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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