3Com 56K Command Reference Manual page 186

I-4 A I: S-R
PPENDIX EGISTERS
Register Default Function
S16 0 Bit-mapped register. (See Chapter 1, Using the AT
Command Set, for instructions on setting bit-mapped
registers.) For testing, see Chapter 14, Testing.
Bit
2
3
S18 0 Test timer for software-initiated loopback testing (&Tn);
disabled when S18 is set to 0. Used to set the duration of
testing, in seconds, before the Business Modem
automatically times out and terminates the test.
S19 0 Sets the duration, in minutes, for the Inactivity Timer. The
timer activates when there is no data activity on the phone
line, and at the timeout the Business Modem hangs up.
S19=0 disables the timer.
S21 10 Sets, in 10-millisecond units, the length of breaks sent from
the Business Modem to the computer or terminal. Applies
to ARQ mode only.
S22 17 Stores the ASCII code for the XON character.*
S23 19 Stores the ASCII code for the XOFF character.*
S24 150 Sets the duration, in 20-millisecond units, between pulsed
DSR signals when the Business Modem is set to &S2 or &S3.
The default is 3 seconds.
S25 5 Sets DTR recognition time in 10-millisecond units.
S27 0 Bit-mapped register. (See Chapter 1, Using the AT
Command Set, for instructions about setting bit-mapped
registers.)
Bit
0
1
2
Value Result
4 Test pattern.
8 Remote digital loopback.
Value Result
1 Enable ITU-T V.21 modulation at 300
bps for overseas calls. In V.21 mode,
the Business Modem answers both
Bell 103 and V.21 calls, but only
originates V.21 calls.
2 Enable unencoded (non- trellis-coded)
modulation in V.32 mode; this option
is part of the ITU-T V.32
recommendation, but is rarely used.
4 Disable V.32 modulation; used for
testing HST modulation.