Low Power V.22 bis Modem
CMX868
Rx Mode Register b8: Rx Auto-equalise (DPSK/QAM modem modes)
This bit controls the operation of the receive DPSK/QAM auto-equaliser. Set to 0 in FSK
modes. Set to 1 in 2400bps QAM mode.
b8 = 1
b8 = 0
Enable auto-equaliser
DPSK mode: Auto-equaliser disabled
QAM mode : Auto-equaliser settings frozen
Rx Mode Register b7-6: Rx Scrambler (DPSK/QAM modem modes)
These 2 bits control the operation of the Rx descrambler used in QAM and DPSK modes.
Set both bits to 0 in FSK modes
b7
b6
1
1
0
1
0
x
Descrambler enabled, 64 ones detect circuit enabled (normal use)
Descrambler enabled, 64 ones detect circuit disabled
Descrambler disabled
Rx Mode Register b5-3: Rx USART Setting (QAM, DPSK, FSK modem modes)
These three bits select the Rx USART operating mode. The 1% and 2.3% overspeed options
apply to DPSK/QAM modes only.
b5
b4
b3
1
1
1
1
0
1
1
0
0
x
1
0
1
0
x
Rx Synchronous mode
Rx Start-stop mode, no overspeed
Rx Start-stop mode, +1% overspeed (1 in 8 missing Stop bits allowed)
Rx Start-stop mode, +2.3% overspeed (1 in 4 missing Stop bits allowed)
Rx USART function disabled
Rx Mode Register b2-0: Rx Data bits and parity (QAM, DPSK, FSK Start-Stop modem
modes)
In Start-stop mode these three bits select the number of data bits (plus any parity bit) in each
received character. These bits are ignored in Synchronous mode.
b2
b1
b0
1
1
1
1
0
0
0
0
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
8 data bits + parity
8 data bits
7 data bits + parity
7 data bits
6 data bits + parity
6 data bits
5 data bits + parity
5 data bits
Rx Mode Register b2-0: Tones Detect mode
In Tones Detect Mode (Rx Mode Register b15-12 = 0001) b8-3 should be set to 000000
Bits 2-0 select the detector type.
b2
b1
b0
1
0
0
0
0
0
1
1
0
0
0
1
0
1
0
Programmable Tone Pair Detect
Call Progress Detect
2100, 2225Hz Answer Tone Detect
DTMF Detect
Disabled
ã 2004 CML Microsystems Plc
27
D/868/9
CMLMICRO [ CML MICROCIRCUITS ]
