ColdFire/68K Microcontrollers and ProcessorsのトピックWhen using mini-flex bus on MCF52259 - do I need to connect pull-up to D0-D7 ?

When using mini-flex bus on MCF52259 - do I need to connect pull-up to D0-D7 ?

ambre — Thu, 12 Jun 2014 07:15:58 GMT

Usually, pull-ups are needed on data bus, but in the MCF52259EVB schematic - no pull-ups are mentioned.

Re: When using mini-flex bus on MCF52259 - do I need to connect pull-up to D0-D7 ?

TomE — Thu, 12 Jun 2014 07:34:34 GMT

Why do you think pullups are required on a data bus?

There are some instances in which this might be useful; I'm interested in your reasons.

Tom

Re: When using mini-flex bus on MCF52259 - do I need to connect pull-up to D0-D7 ?

ambre — Thu, 12 Jun 2014 07:55:31 GMT

Usually pull-ups are required on data bus, to make a legal voltage levels between access to the different devices on the bus.

Unless the devices on the data bus have internal pull-ups.

Re: When using mini-flex bus on MCF52259 - do I need to connect pull-up to D0-D7 ?

TomE — Thu, 12 Jun 2014 23:24:44 GMT

> legal voltage levels between access to the different devices on the bus.

Between accesses, no device cares what the levels are on the bus, so it doesn't really matter.

You haven't given me your specific reasons for wanting "legal voltage levels" between cycles.

Or why the EVB should be supporting and demonstrating that need or requirement.

Tom

Re: When using mini-flex bus on MCF52259 - do I need to connect pull-up to D0-D7 ?

miduo — Mon, 16 Jun 2014 08:28:03 GMT

Typically, since the data lines can be inputs it is best not to have them floating at any time. However, we don't use pullups/downs on the data buses on our ColdFire eval boards.