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reading data from a FT245BM

Started by orionsem January 22, 2009
Hello, 
I am totally new to USB (well, at least to the darkness inside ;-(
I have to read data from an FPGA located behind the TD245. My question is
: who begins the data transfer? if I program the FPGA to read say 1k bytes,
does the FPGA have to begin filling up the FIFO and suppose that the data
will be caught on time by the DLL, or does the FPGA have to track the TXE
("transmit enable") and respond each time?
Sorry for the beginner's status... and many many thanks for the future
replies :-)
Jean Louis


In article <yrCdndXaPfEDk-TUnZ2dnUVZ_qvinZ2d@giganews.com>, 
support@orionmicroscopy.com says...
> Hello, > I am totally new to USB (well, at least to the darkness inside ;-( > I have to read data from an FPGA located behind the TD245. My question is > : who begins the data transfer? if I program the FPGA to read say 1k bytes, > does the FPGA have to begin filling up the FIFO and suppose that the data > will be caught on time by the DLL, or does the FPGA have to track the TXE > ("transmit enable") and respond each time?
I think you are mixed up about the control signals of the FT245. Your FPGA sends bytes to the FT245 until the TXF# signal tells it to stop---which it will do when the FIFO is full. The FT245 uses the bulk transfer mode, and it will tell your FPGA to not send more data until the PC (or other host device) on the other end of the USB link takes some bytes. I'm not totally clear on whether the FPGA is primarily sending bytes or receiving---but it works the same way as far as the FPGA is concerned.
> Sorry for the beginner's status... and many many thanks for the future > replies :-) > Jean Louis >
Mark Borgerson