Re: When to use a 74LS245 to buffer the data bus?

["Glenn Jones" <rg.jones@rogers.com>]

"GSGeek sympatico.ca>" <yves.mcdonald@<NO_SPAM> wrote in message
news:wYuta.538$J%5.147813@news20.bellglobal.com...
> Hello,
>
> The 74LS245 is a bidirectionnal bus transceiver with 3-state output.
> Depending on the signals present on G* and DIR pins, the chip can let data
> bits flow trough its 8 bidirectionnal buffers (G* held high) or disconnect
> from the Apple data bus (G* held low). The chip can 'disconnect' by
putting
> all its ouputs into high impedance.   The transceiver is useful to
interface
> a device chip with bidirectionnal data bits  which can't go into high
> impendance.
> The transceiver is also useful to increase the fanout of data input
signals.
> The Apple 2 bus' D0..D7 signals can only drive a few TTL inputs (less than
> five I believe) per card.
> In a nutshell, you won't need one if you have a few chips tied to the data
> bus and if each one of them can have their data output signals go into
high
> impedance (disconnects from the bus).
>
> Happy hardware hacking - it's fun!
>
> Yves
>
> "Glenn Jones" <rg.jones@rogers.com> a �crit dans le message news:
> Ydtta.106779$kYH.10128@news01.bloor.is.net.cable.rogers.com...
> > During the design of  an adapter card for the Apple II  when is it
> > appropriate to use a 74LS245 to buffer the data bus? I see some designs
> that
> > use this chip and others that don't, so I am not sure if I need to use
> one?
> >
> > Any input would be appreciated.
> >
> > Thank You
> >
> > Glenn
> >
> >
>
>

Yves, I am interfacing an ethernet module to the Apple2 bus. The module has
two chips on it...one is a custom chip W3100A and the other is a RTL8201L
PHYceiver chip. I am not sure how many TTL inputs this would be equivilent
too.

The concept is the same as the TFE ethernet board that Adam Dunkels created
except that the Wiznet chip is amost 1/4 the price and has a TCP/IP stack
built into the 3100A.

I have a prototype wired up without the 74LS245 but IIgs hardware reference
pg 180 talks about loading and driving rules and this has got me thinking
htat maybe I should be using a 74LS245 for the data bus.

If you are interested, you can find out more information about my project at
http://members.rogers.com/rg.jones/AppleII_ethernet%20_project.htm

Thanks

Glenn