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'[PIC]:FTDI FT245BM bus sharing?'
2003\07\21@085115 by ?Graham=20North?=

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Has anyone had success using the FT245BM?

I am trying to use it in a prototype design, but am wanting to share the data bus with other peripherals (e.g. LCD). I have the device self powered as per the user guide. The problem I can see is that as soon as the USB cable is plugged in, the chip will come out of reset and its data bus pins will not be tristated, and I won't be able to share the data bus with any other device.

Thanks

Graham



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2003\07\21@092523 by Peter Moreton

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Graham, I had the same dilemma; wanted to put a FT245 onto the PSP bus
of a PIC, and also run a parallel ADC onto the PSP as well. Reading the
datasheets, I could not convince myself that bus contention problems
would not occur, and ended up putting the parts onto separate busses. I
suggest an email to FTDI's product support might be worthwhile, and I'd
be interested to hear what they say.
Regards, Peter Moreton


{Original Message removed}

2003\07\21@100354 by ?Graham=20North?=

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Hi Peter,

I have sent their support department two emails on the subject with no reply :-(
I'm starting to think the same as you.

Graham

Peter Moreton <spam_OUTpeterTakeThisOuTspamRIL.ORG.UK> wrote:
Graham, I had the same dilemma; wanted to put a FT245 onto the PSP bus
of a PIC, and also run a parallel ADC onto the PSP as well. Reading the
datasheets, I could not convince myself that bus contention problems
would not occur, and ended up putting the parts onto separate busses. I
suggest an email to FTDI's product support might be worthwhile, and I'd
be interested to hear what they say.
Regards, Peter Moreton


{Original Message removed}

2003\07\21@104504 by Ken Pergola

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Hi Graham,

The FT245xM's bus is *only active* when RD# is asserted and is tristated
otherwise.

When you want to share the bus, you must make sure RD# is not asserted.

Best regards,

Ken Pergola




{Original Message removed}

2003\07\22@071234 by ?Graham=20North?=
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Ken, have you successfully used this chip as you describe?

Thanks

Graham

Ken Pergola <.....no_spamKILLspamspam@spam@LOCALNET.COM> wrote:
Hi Graham,

The FT245xM's bus is *only active* when RD# is asserted and is tristated
otherwise.

When you want to share the bus, you must make sure RD# is not asserted.

Best regards,

Ken Pergola




{Original Message removed}

2003\07\22@151340 by Ken Pergola

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Hi Graham,

How are you coming to the determination that the bus is not tri-stated?

Don't forget that the data bus and control signals have internal pullups (I
believe FTDI told me that value is approximately 200K ohms).

I'm finding out they are tri-stated when RD# is not asserted (+5V with
respect to ground). If I short a data line to ground (while RD# is not
asserted) I'm measuring 0.028 mA which confirms that it is tri-stated and
support's FTDI claim about the 200K ohm pullups.

Regarding your question about sharing the bus:
I haven't yet the need to share the bus so I have not tried it personally --
the information I posted was information given to me by FTDI.

Please give us some more details and let us know what you find out.

Best regards,

Ken Pergola



{Original Message removed}

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