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Host-Based Controller Modem Data Addendum
AT Command Set June 15, 1998
AT Commands Reference S-Registers (continued)
Lucent Technologies Inc. Version 1.0
34
S38 K56flex Downstream Rate
To force a particular K56flex downstream rate, use S-register S38. S38=0 disables K56flex, and may allow a
more reliable V.34 connection. S38=1 default allows the modem to select the downstream rate automatically.
Other values of S38 force the downstream rate, with fallback to V.34 if unsuccessful at the configured rate:
S38=0 Disable K56flex
S38=1 Automatic rate selection (default)
S38=2 32 kbit/s
S38=3 34 kbit/s
S38=4 36 kbit/s
S38=5 38 kbit/s
S38=6 40 kbit/s
S38=7 42 kbit/s
S38=8 44 kbit/s
S38=9 46 kbit/s
S38=10 48 kbit/s
S38=11 50 kbit/s
S38=12 52 kbit/s
S38=13 54 kbit/s
S38=14 56 kbit/s
The number of robbed-bit signaling (RBS) frames detected decreases the true DCE rate per the following table:
RBS links
Rate hit (kbit/s)
0 0
1 2
2 4
3 4
4 6
5 8
6 8
For example, if S38=10 and there are 3 RBS links, the K56flex downstream rate will be 48-4=44 kbit/s. The
exception to this is for 32 kbit/s and 34 kbit/s, which are the true rates regardless of the number of RBS frames
detected.
One special value of S38, S38 = 251, is used for back-to-back (factory) testing of V.34 rates, with DSP code
running in external memory. Set S38=251 on both originating and answering modems. (This feature is not valid
with ramless solution.)
S42 Auto Rate (default 1, range 01)
This command is used for testing and debugging only.
V.32bis and V.22bis auto rate is disabled. Retrain operation is disabled or enabled in data mode, and fallback is
disabled in data mode. In K56flex mode, S42=0 forces connection at the rate specified by S38 (even if the rate
cannot be sustained), without fallback to V.34.
0 = auto rate disabled, 1 = enabled.
Range: 0—1
Default: 1