Robert E. Griffith wrote:
>>> The limitation for 150kbps here is related to the PC serial
>>> port itself, that simply can not talk faster than this.
>
> The FTDI virtual serial port USB driver does not actually use the PC
> serial port hardware (that's what makes it virtual:).  As long as
> your PC software allows selected a higher baud rate, the software
> driver will do it.

Yes, but most of the time, your PC software will not even know it is
talking via USB, since it was written to drive a real COM: port, you just
change the address from COM1: to COM4: for example.  Everything else in the
software still thinking it still  to be a real COM port, including top
speed parameters.


> The limitation is the single ended serial connection between the FTDI
> chip and your hardware.  Since the FTDI chip is physically close to
> your device, you can get away with higher rates than in the general
> case where a cable might be 10's or 100' of feet long.  Of course, as
> you pointed out the firmware needs to be able to select a higher rate.
>
> The Rabbit dev kit I have (RS232 serial peripheral --> FDTI eval
> cable --> FDTI virtual serial port driver) runs at something like 240
> baud.  If you succeed in convincing me that it can't be done, I will
> stop using it as I would not want to violate any laws of physics:)

You mean 240kbps, not 240bps, right?  (240 bps would be as fast as 20 chars
/second).  For sure, if the PC software knows that in true it is NOT
talking to a real UART at the motherboard, then it can reach any speed it
wants, probably limited by the hardware on board, in this case, the USB
driver and hardware.  I was talking about PC software that doesn't know it
is using USB.  Suppose for instance you have an old Windows Terminal
program that would access a modem at COM1:  When you install the FTDI
windows drivers, probably it will allow you to use the Terminal program
connecting to a COM4 or COM5. If at the end of the USB you have a FTDI and
then a modem at the FTDI serial pins, then the Terminal program will still
programming COM5 top speed as the maximum speed it has at the selection
menus, in this case, hopefully, 38400 or 57600bps max. So, even that the
on-board USB hardware can communicate faster, it will in true transfer data
to the FTDI chip at 38400 or 57600 bps, it transfer faster, but the
effective bytes/second transfered will be this, since this is the speed the
Terminal program will deliver data to the FTDI windows driver.

Wagner Lipnharski - email:  wagner@ustr.net
UST Research Inc. - Development Director
http://www.ustr.net - Orlando Florida 32837
Licensed Consultant Atmel AVR _/_/_/_/_/_/

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