Low Power V.22 bis Modem
CMX868
Tx Mode Register b7-5: DTMF Twist (DTMF mode)
These 3 bits allow for adjustment of the DTMF twist to compensate for the frequency
response of different exernal circuits. Set b8 to 0. The device varies the twist by making
changes to the upper tone group levels. Note that the twist cannot be adjusted mid-tone.
b5
b7
b6
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
+2.0dB twist (normal setting when external response is flat)
+1.0dB twist
+1.5dB twist
+2.5dB twist
+3.0dB twist
+3.5dB twist
+4.0dB twist
+4.5dB twist (do not use in conjunction with the 0dB tx level
setting).
Tx Mode Register b8-7: Tx Guard tone (QAM, DPSK modes)
These 2 bits select the guard tone to be transmitted together with highband QAM or DPSK.
Set both bits to 0 in FSK modes.
b8
b7
1
1
0
1
0
x
Tx 550Hz guard tone
Tx 1800Hz guard tone
No Tx guard tone
Tx Mode Register b6-5: Tx Scrambler (QAM, DPSK modes)
These 2 bits control the operation of the Tx scrambler used in QAM and DPSK modes.
Set both bits to 0 in FSK modes.
b6
b5
1
1
0
1
0
x
Scrambler enabled, 64 ones detect circuit enabled (normal use)
Scrambler enabled, 64 ones detect circuit disabled
Scrambler disabled
Tx Mode Register b4-3: Tx Data Format (QAM, DPSK, FSK modes)
These two bits select Synchronous or Start-stop mode and the addition of a parity bit to
transmitted characters in Start-stop mode.
b4
b3
1
1
0
0
1
0
1
0
Synchronous mode
Start-stop mode, no parity
Start-stop mode, even parity bit added to data bits
Start-stop mode, odd parity bit added to data bits
ã 2004 CML Microsystems Plc
23
D/868/9
CMLMICRO [ CML MICROCIRCUITS ]
