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Omni 56K II and Omni 56K Plus II User’s Guide
3-6 Specifications and Functions
3.9 Software XON/XOFF Flow Control
This is a bi-directional flow control. XON and XOFF character defaults are decimals 17 and 19. These can be
changed by modifying the S-Registers S31 and S32.Both the modem and the DTE will treat XOFF as a
signal to stop transmitting data and will treat XON as a signal to restart sending data. Modems will not send
these characters received from the local DTE to the remote modem.
3.10 Error Control
Error control keeps the modem data link error-free by detecting and re-transmitting erroneous data. The
Omni 56K II and Omni 56K Plus II modems support both MNP and V.42 error control protocols. The MNP
protocol was an industry standard developed and licensed by Microcom, Inc. Omni 56K II and Omni 56K
Plus II modems support level 4 and 3 error control protocols, commonly denoted as MNP4 and MNP3. V42
is a standard developed by CCITT. V.42 supports both LAPM and MNP4. A V.42 handshake will try an
LAPM connection first, and if it is not successful, it will try MNP4.
3.11 Data Compression
In the modem, the data compression is activated to reduce the number of bits actually sent. The receiving
modem applies these techniques in reverse to recover the actual data from the compressed data stream.
The Omni 56K II and Omni 56K Plus II modems support V.44, V.42bis and MNP5 data compression
protocols. Data compression needs an error-free data link to work correctly, otherwise the corrupted
compressed data stream will ruin the decompression process. MNP5 is used with MNP4 error control, V.44
and V.42bis are used with V.42 error control. The compression efficiency of V.42bis is generally higher than
that of MNP5.
3.12 Repeat Dial
The modem will dial the default number stored in non-volatile RAM, EEPROM, repeatedly if not connected.
(s38.0=1,*Dn)
3.13 Cyclic Dial
Dial the number stored in EEPROM at location n(0-3) if cyclic dial s44.3=1 is set. If the first dial is not
successful, the modem will cycle dial through the four numbers stored in memory.