3Com 56k User's Manual And Reference page 68

Register Default
S13 (Continued)
S14 0
S15 0
64
Technical Reference
Function
Bit Value Result
5 32 Reserved
6 64 Disable quick retrains
7 128 Disconnect on escape code
*The 1.5K-byte non-ARQ buffer allows data transfer with Xmodem- and Ymodem- type file
transfer protocols without using flow control
The 128-byte option lets remote users with slower modems keep data you are sending from
scrolling off their screens
When remote users send your computer an Xoff (Ctrl-S) and you stop transmitting, the data in
transit from your modem's buffer does not exceed the size of their screen
This is also very helpful in situations when a remote modem/printer application is losing
characters
Reserved
Bit-mapped register setup
To set the register, see instructions for S13
Bit Value Result
0 1 Disable ARQ/MNP for V.22
1 2 Disable ARQ/MNP for V.22 bis
2 4 Disable ARQ/MNP V.32/V.32 bis