Guidelines - US Robotics COURIER User Manual

COURIER HIGH SPEED MODEMS
NOTE: You may have to set your software as well to either
hardware or software flow control. Some programs also require
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that you turn off the type you are not using. -
&HO Transmit Data flow control disabled. Default.
&H1 Hardware flow control. Recommended setting. Requires -
that your DTE and software support Clear to Send (CTS)
at the RS-232 interface.
&H2 Software flow control. Requires that your software
support XON /XOFF signaling. See the guidelines that
follow. The ASCII characters may be user-defined. See
Registers S22 and S23 in Appendix B. That appendix also
includes an ASCII chart.
&H3 Use both hardware and software flow control. If you are
unsure about what your equipment supports, select this
option. But keep the warning, above, in mind about
software flow control.
WARNING: If possible, always use hardware flow control. You
may lose data if XON /XOFF characters occur in the data stream
from other sources. They may, for example, come from the
remote system: an XON from the remote system, after your
modem has sent an XOFF, can result in buffer overflow.
Ctrl-S (XOFF) and Ctrl-Q (XON) characters also occur in binary
files, and are used by Xmodem-type protocols. You risk having
these characters misinterpreted as modem flow control charac-
ters and dropped from the data stream.
Guidelines
If your terminal or software does not support Clear to Send, use
of software flow control may prove satisfactory if you're only
transferring text files.
However, if you're transferring non-text (binary) files, or using
an Xmodem-type protocol, disable flow control entirely (&HO).
In addition, be sure the modem is set to &BO and &NO, so that
the DTE and link rates are equal.
4-8 Interface Controls
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