libftdi Archives

Subject: RE: Bit Bang mode hardware bug for FT232 and FT2232 chips

From: "Spindler, Tyler L" <TLSpindler@xxxxxxxxxxxxxxxxx>
To: <libftdi@xxxxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 17 Jun 2010 09:37:04 -0500
>> What I don't understand and contradicts my scope measurements is the 
>> "baud rate * 16": In my application it works pretty well with baud rate 
>> * 8! At least if I use a baud rate of 65536 I get pretty good results 
>> for the pulse/pause length I need (220 to 3000 µs).
>> Keep us up-to-date with your findings about the FT2232H so maybe next 
>> time I can really only use one of these chips instead of an extra timer.
>I have also had the best success with setting the baud rate to 65536 when
>writing (thanks to Albert Huitsing's site,
>I am getting baud rates x16 when I write, unlike the baud rate of x8 like
>you indicate.  Could be because of the missed ticks do to the error below.
>Also, the baud rate will be different if you set it before you put the chip
>into BitBang mode vs. after you put it into BitBang mode... make sure you
>set the baud rate after.  Myself... I got different read buffer rates from
>different chips.  For the FT232R I got x32 the baud rate and from FT2232D
>I got x16 the baud rate.  I was using version 0.17 of libftdi.  Not sure
>why, but those were my results.

I got the FT2232H chip in yesterday and tested it in BitBang mode overnight.
I'm happy to report that it has been 100% reliable thus far and appears to be
consistently clocking data in and out.  If you plan to use bit bang mode and
require consistent and accurate clocking, I'd recommend this chip and not
the FT232R and FT2232C/D chips.

One weird thing, I'm getting 80x the baud rate I'm setting using libftdi 0.17
when the chip is in BitBang mode. Are there known issues setting the baud
rate with this chip?  Looking at the change log, the 0.17 version supports
the FT2232H chip baud rate format and was just added in the latest version.


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