GMSK Packet Data Modem and RF Transceiver
CMX990
Control Register B7, B6: AGC Control
These two bits have no effect in transmit mode.
In receive mode these bits set the response of the AGC circuit. The 'Run' and 'Max Gain and
Run' settings allow the circuit to acquire and track incoming signals.
B7 B6
Setting
Max Gain and Hold
Hold*
Action
0
0
1
1
0
1
0
1
AGC set to maximum gain and held
AGC gain not updated by internal circuit
AGC tracks input signal
Run
Max Gain and Run
AGC set to maximum gain and tracks input signal
* Host may override AGC setting by writing to $19 only when this setting is selected.
Control Register B5, B4: I/Q Offset Control
These two bits have no effect in transmit mode.
In receive mode, these set the ‘normal’ response of the I/Q offset measuring circuits. The
offset control is in two sections, an analogue 'coarse' setting and a digital 'fine' setting. The
host may read and directly overwrite the coarse setting via registers $18 and $19. The coarse
and fine settings will be overridden by the Acquire I Q Offset command (bit 6 of Command
register) which will go through a sequence of:
Reset
Run with Coarse Tracking for 12 bits to correct gross I/Q offset error
Run with Fine Tracking for 640 bits to adjust for remaining I/Q offsets
Revert to normal setting (hold / fine / coarse)
B5 B4
Setting
Reset and Hold
Hold*
Fine Tracking*
Coarse Tracking
Action
I/Q offset tracking reset and held
I/Q offset tracking held at current setting
I/Q fine offset tracking
0
0
1
1
0
1
0
1
I/Q coarse offset tracking
* Host may override Coarse I/Q Offset by writing to registers $18 and $19 only when these settings are
selected and bit 6 of Command register is = '0'.
Control Register B3, B2: Frequency tracking (AFC) Control
These two bits have no effect in transmit mode.
In receive mode, they set the ‘normal’ response of the frequency tracking circuits. This setting
will be temporarily overridden by the Acquire AFC command (bit 5 of Command register) which
will go through a sequence of:
Reset
Run with Fast Tracking for 96 bits to correct frequency offset error
Run with Slow Tracking for 750 bits to follow any further frequency offsets
Revert to normal setting (hold / slow / fast)
B3 B2
Setting
Reset and Hold
Hold
Slow Tracking
Fast Tracking
Action
Frequency tracking reset and held
Frequency tracking held at current setting
Frequency slow tracking
0
0
1
1
0
1
0
1
Frequency fast tracking
For Mobitex systems, and most general purpose applications using the modem, these bits
should normally be set to Slow Tracking after the host has activated the automatic sequence.
ã 2004 CML Microsystems Plc
31
D/990/1
CMLMICRO [ CML MICROCIRCUITS ]
