Low Power V.22 bis Modem
CMX868
1.5.10.2 General Control Register
General Control Register: 16-bit write-only. C-BUS address $E0
This register controls general features of the CMX868 such as the Powersave and Loopback modes, the
IRQ mask bits and the Relay Drive output. It also allows the fixed compromise equalisers in the Tx and
Rx signal paths to be disabled if desired, and sets the internal clock dividers to use either a 11.0592 or a
12.288 MHz XTAL frequency.
All bits of this register are cleared to 0 by a General Reset command.
15
0
14
0
13
0
12
11
10
9
8
7
6
5
4
3
2
1
0
Bit:
Xtal
freq
LB
Equ
Rly
drv
Pwr
Rst
Irqn
en
IRQ Mask Bits
General Control Register b15-13: Reserved, set to 000
General Control Register b12: Xtal frequency
This bit should be set according to the Xtal frequency.
b12 = 1
b12 = 0
11.0592MHz
12.2880MHz
General Control Register b11: Analogue Loopback test mode
This bit controls the analogue loopback test mode. Note that in loopback test mode both
Transmit and Receive Mode Registers should be set to the same modem type and band or bit
rate.
b11 = 1
b11 = 0
Local analogue loopback mode enabled
No loopback (normal modem operation)
General Control Register b10: Tx and Rx Fixed Compromise Equalisers
This bit allows the Tx and Rx fixed compromise equalisers in the modem transmit and receive
filter blocks to be disabled.
b10 = 1
b10 = 0
Disable equalisers
Enable equalisers (600, 1200 or 2400bps modem modes)
General Control Register b9: Relay Drive
This bit directly controls the RDRVN output pin.
b9 = 1
b9 = 0
RDRVN output pin pulled to VSS
RDRVN output pin pulled to VDD
ã 2004 CML Microsystems Plc
20
D/868/9
CMLMICRO [ CML MICROCIRCUITS ]
