AW: AW: [OpenBIOS] OT: Bios access speeds

[Matthias Wächter]

On Fri, 30 Apr 1999, Stephan Müller wrote:

> > > You can take a small ISA-prototype-card and a address-decoder (e.g.
> > > 74HC245).
> > Sorry, the 74HC245 is no address decoder, it's an 8 bit parallel buffer
> > driver (usually used for the data bus).
> Hm, what else is used? I can only see this 74245 everywhere... :)

Well ... I can't answer that in general. You will see the 74(xx)245 on
various ISA-Boards, because it is needed to be there. The ISA Bus is not
capable of driving that much input pins (of every ISA card) in parallel,
so transceivers are (to be) used which are only switched on (and thus
loading the bus) if the device is selected. Additionally it is used to
multiplex address and data bus for some chips multiplexing these signals.

Anyway, the '245 is nothing more than an enablable two-way amplifier.

> > You will need a real address decoder for that. If size is the problem, use
> > a GAL.
> or so. :)

Well, my TTL times are gone for long, so I can't tell you a type number
from my mind. But anyway, GALs are really cheap nowadays and one can place
it on a socket to reuse it in any other, different place and application.

Sehr Wus,
- Matthias

-- 
Bunt ist das Dasein und granatenstark. Und: Volle Kanne, Hoschis!
                         aus: "Bill und Teds verrückte Reise durch die Zeit"
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