Looking for dialup hardware solution

phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org
Sun Jul 13 02:25:41 UTC 2008

> 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.

Peter Hiscocks
Syscomp Electronic Design Limited, Toronto
USB Oscilloscope and Waveform Generator

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