Re: ROMs replacement

From: Segher Boessenkool <>
Date: Tue, 18 Sep 2012 00:44:48 +0200
Message-Id: <>
>>> They are not really tristate in the 6502.
>> This here says otherwise:
> Where is the contradiction? The output (data output register, DOR) is
> connected to the external data bus with tristate buffers. Note that  
> this
> is an output.
> OTOH, the predecode register (PD) and input data latch (DL) are always
> connected to the external data bus. Thus, they sink any current  
> that is
> on the external data bus.
> Thus, the data bus is not really tristate.

A MOS input does not sink any significant current.  Typical is 2uA for
a normal input, and 10uA for a tristate input (it leaks more via the
disabled output driver than via the input itself!)


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Received on 2012-09-17 23:00:05

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