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

["GSGeek" <yves.mcdonald@<NO_SPAM>sympatico.ca>]

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
>
>