SN74ACT245DW bit flipping

Mena Roumbakis

Prodigy 100 points

Using the SN74ACT245DW under the following conditions:

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OEn = low

DIR = low (bus B to bus A operation)

bus B = not actively driven (connected to ISA bus w/ other boards)

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During this state there is some activity/bit flipping on bus B even though it is not being driven. Under these same circumstances there are no issues when using the Fairchild 74ACT245SC. What could be causing the bit flipping?

over 14 years ago

0 Edwin Krasser over 14 years ago

Expert 2420 points

Hi!

"no actively driven": Does this mean floating? Or is there a pulk up resistor?

Best regards,
Edwin Krasser

0 Mena Roumbakis over 14 years ago in reply to Edwin Krasser

Prodigy 100 points

Floating. Not sure about the ISA backplane though.

-Mena

0 Edwin Krasser over 14 years ago in reply to Mena Roumbakis

Expert 2420 points

If it's floating it's floating and you will not get a defined logic value. Hence, a change of the logic level is quite normal (interference from mains, other devices, ...). Is this something you just see on the scope or does it interfere the bus function too?

Best regards,
Edwin Krasser

Logic

Logic forum

SN74ACT245DW bit flipping