3Com 1.024.1644-00 - Manual (Page 74)

Technical Reference
68 56K Voice Faxmodem Internal - User’s Guide
Register Default Function
S19 0 Sets the duration, in minutes, for the inactivity timer. The
timer activates when there is no data activity on the phone
line; at time-out the modem hangs up. S19 = 0 disables
the timer.
S20 0 Reserved
S21 10 Sets the length, in 10-millisecond units, of breaks sent
from the modem to the computer; applies to MNP or
V.42 mode only.
S22 17 Stores the ASCII decimal code for the XON character.
S23 19 Stores the ASCII decimal code for the XOFF character.
S24 0 Reserved
S25 20 Sets the duration, in hundredths of a second, that DTR
must be dropped so that the modem does not interpret a
random glitch as a DTR loss. (Most users will want to use
the default; this register is useful for setting compatibility
with older systems running under older operating software.)
S26 0 Reserved
S27 0 Bit-mapped register setup. To set the register,
see instructions for S13.
Bit Value Result
0 1 Enables ITU-T V.21 modulation at 300
bps for overseas calls; in V.21 mode,
the modem answers both overseas
and domestic (U.S. and Canada)
calls, but only originates V.21 calls.
(Default Bell 103)
1 2 Enables unencoded (non-trellis
coded) modulation in V.32 mode.