There’s a known bug with the 232R chip (maybe the 245R chip to) that the data buffer doesn’t always clock out data in the buffer at the proper rate. It’ll miss a tick here
and here and it is seemingly random. I recommend using the H version of the chips. Here’s the thread about it.
http://libftdi.141977.n3.nabble.com/Bit-Bang-mode-hardware-bug-for-FT232-and-FT2232-chips-td889096.html
From: Giampaolo Bellini [mailto:iw2lsi@xxxxxxxxx]
Sent: Friday, July 01, 2011 3:34 AM
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Subject: bitbang on FT232R / FT245R
Hi all
I'm new to (lib)ftdi and I'm experimenting with bitbang mode using two modules from DLP-Design to communicate with an external device via I2c
my doubts are about the "stability" of the generated frames... as I see a lot of jitter on SCL and SDA, even when working at a low baudrate.
the whole test frame is prepared offline and then sent via one (and only one) ftdi_write_data() call.
my lines are pulled-up with 4.7K resistors to 5VCC as the module is usb-self-powered.
I know that it should work even with such jitter but... is this normal or I'm missing something ?
thanks a lot for any hints
Giampaolo
libftdi - see http://www.intra2net.com/en/developer/libftdi for details.
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