3Com 56k User's Manual And Reference page 73

Register Default
S34 (Continued)
S35-S37
S38 0
S39-S40
S41 0
S42 0
Technical Reference
Function
Bit Value Result
2 4 Disable 32S-2D trellis encoding
3 8 Disable 64S-4D trellis encoding
4 16 Disable non-linear coding
5 32 Disable TX level deviation
6 64 Disable Pre-emphasis
7 128 Disable Pre-coding
Reserved
Sets an optional delay, in seconds, before a forced hang-up and clearing of the Transmit buffer
when DTR drops during an ARQ call. This allows time for a remote modem to acknowledge
receipt of all transmitted data before it is disconnected. The modem immediately hangs up
when DTR drops.
This option only applies to connections terminated by dropping DTR. If the modem receives
the ATH command, it ignores S38 and immediately hangs up.
Reserved
Reserved
Reserved
69