Post by thread:[PIC]:FTDI FT245BM bus sharing?

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 --------------------------------- Want to chat instantly with your online friends? Get the FREE Yahoo!Messenger -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

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}

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_OUTpeterTakeThisOuTRIL.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}

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}

Ken, have you successfully used this chip as you describe? Thanks Graham Ken Pergola <.....no_spamKILLspam@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}

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}