GMSK Packet Data Modem
CMX909B
1.5.4.4 Mode Register
The contents of this 8-bit write only register control the basic operating modes of the modem:
Mode Register B7: IRQNEN - IRQN Output Enable
When this bit is set to ‘1’, the IRQN chip output pin is pulled low (to V ) whenever the IRQ bit of
ss
the Status Register is a ‘1’.
Mode Register B6: INVBIT - Invert Bits
This bit controls inversion of transmitted and received bit voltages. When set to ‘1’ all data is
inverted in the Tx and Rx data paths so a transmitted '1' is a voltage below V
at the TXOP pin
BIAS
and a received '0' is a voltage above V
this bit is set to ‘1’.
at the RXIN pin. Data will be inverted immediately after
BIAS
Mode Register B5: TXRXN - Tx/Rx Mode
Setting this bit to ‘1’ puts the modem into Transmit mode, clearing it to ‘0’ puts the modem into
Receive mode. When changing from Rx to Tx there must be a 2-bit pause before setting a new
task to allow the filter to stabilise. (See also PSAVE bit).
Note that changing between receive and transmit modes will cancel any current task
Mode Register B4: SCREN - Scramble Enable
The scrambler only takes effect during the transmission or reception of a Mobitex Data Block, Short
Data Block and during a TSO task. Setting this bit to ‘1’ enables scrambling, clearing it to ‘0’
disables scrambling.
The scrambler is only operative, if enabled by this control bit, during TSO, RDB, RSD, TSD or TDB,
it is held in a reset state at all other times.
This bit should not be changed while the modem is decoding or transmitting a Mobitex Data Block.
Mode Register B3: PSAVE - Powersave
When this bit is a ‘1’, the modem will be in a ‘powersave’ mode in which the internal filters, the Rx bit
and Clock extraction circuits and the Tx o/p buffer will be disabled, and the TXOP pin will be
connected to V
through a high value resistance. If the PSBias or PSBiXt bit patterns are set in
BIAS
the Command Register, the V
and Xtal/Clock circuits will be powersaved in accordance with the
BIAS
description in section 1.5.4.2. Setting the PSAVE bit to ‘0’ restores power to all of the chip circuitry.
Note that the internal filters will take about 2 bit times to settle after the PSAVE bit is taken from ‘1’ to
‘0’.
ã 2001 Consumer Microcircuits Limited
28
D/909B/1
CMLMICRO [ CML MICROCIRCUITS ]
