AIS Baseband IC with/without RF Synthesiser
CMX7032/CMX7042
Tx Timing
PA Ramp &
Modulation
Time
CSTDMA
Wait
Sensing
Figure 9 Tx Burst Timing
If CSTDMA sensing has been enabled then the CMX7032/CMX7042 will measure the carrier level (RSSI)
on the selected channel during the window specified in the transmit timing table. If the user-specified
threshold is exceeded then the subsequent events (RAMDAC, Tx Enable and modulation) will be
cancelled. The threshold is set using the CS_Threshold register, $C2. See User Manual section 9.16 for
details. The device will output a pulse on the CS-SYNC pin, co-incident with the SLOTCLK, when it intends
to attempt a transmission. This is provided to simplify testing under IEC 62287-1 section 12.2.1. The signal
will return to its inactive state when the TxDone task is executed, either as a result of a CS abort or if the
transmission succeeded.
7.4.7 Rx Timing
The CMX7032/CMX7042 has a powersaving mode, where it spends most of its time ‘asleep’, but ‘wakes
up’ at the start of each AIS slot and receives for long enough to determine whether a burst is present or
not. If no burst is received the CMX7032/CMX7042 will make a pair of RSSI measurements and then go
back to sleep. This power saving operation can be turned on and off using the Sleep Mode En bit in the
Mode register, $C1. The CMX7032/CMX7042 will still respond to C-BUS accesses when ‘asleep’ but the
latency between a task being issued and completed may be longer than normal.
The times to perform RSSI measurements, go to sleep, and wake up are configured by the host, and all
times are referenced to the SLOTCLK signal. The host should ensure that these timings result in the
CMX7032/CMX7042 being awake in time to sample the next SLOTCLK signal. The timings are set up
using the Sleep_Timing Config task. See User Manual section 9.19.2.8 for details.
If Sleep mode is not enabled, then the demodulator will run continuously and update the Rx Data buffer
whenever valid data is received.
2012 CML Microsystems Plc
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D/7032/42_FI1.2/13
CMLMICRO [ CML MICROCIRCUITS ]
