[BBC-Micro] Reversing the Tube ULA (destructively)

John Kortink kortink at inter.nl.net
Wed Oct 27 22:36:02 BST 2010


On Wed, 27 Oct 2010 22:26:20 +0100, "J.G.Harston" <jgh at mdfs.net>
wrote:

>John Kortink wrote:
>
>[...]
>
>> In practice, though, DRQ is the inverse of nNMI.
>> But DRQ cannot be disabled, while NMI can (with the M config bit).
>
>...so leaving it off a reimplementation is only saving a
>couple of gates or so. (one latch, one AND?)

Yes. But properly implementing nDACK can be more involved
(depending on the logic chip) due to timing issues. Maybe
the ARM evaluation system uses it.


John Kortink

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