Looking for dialup hardware solution

James Knott james.knott-bJEeYj9oJeDQT0dZR+AlfA at public.gmane.org
Sun Jul 13 12:04:34 UTC 2008

phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org wrote:
>> There are some USB-to-DB9 serial adaptors but I don't know how well they
>> handle the complexities of RS-232 modem control.
> For what it's worth, we found that USB-Serial control includes hardware
> flow control (RTS-CTS handshaking).
> We also found that the FTDI FT232BM chip - which we use in our hardware to
> translate the USB signals back to RS-232 - does not stop instantaneously
> on de-asserting the handshaking line - few more bytes dribble in. (We
> hypothesise that the FT232BM chip is implemented with a microprocessor
> core and the software takes some time to respond to the hardware control
> line.)  However, that's an idiosyncracy of that particular chip, the
> handshaking seems to work fine in the host.
FWIW, I've never seen a UART that actually stops the data on hardware 
handshaking.  Changing those status lines only change status a bit and 
generate an interrupt.  It's up to the software to stop the data.

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