AIS Baseband IC with/without RF Synthesiser
CMX7032/CMX7042
7.7.4 Receive Example
The following detailed example describes the process of receiving an AIS message in Burst mode, on Rx
channel 1.
Table 9 AIS Burst Receive Example
Cmd Reg
Rx1B
OVF
0
Description
DataTask R1BRDY
Free
1
1
2
The host should ensure that the R1BRDY, Data task and
CmdReg Free bits are set.
The host issues an RXB1 Modem task to receive an AIS
burst. Note that the Rx Burst mode bit must be set.
Device executes the Modem task
Device waits for a training sequence and start flag, then
begins to demodulate and decode data. The Rx state
changes from Idle to receiving. If the burst has a correct
CRC, the result is placed in the data buffer, if not, it is
discarded. An Rx State Change is issued and the Rx state
changes from receiving to idle, or an error condition.
The host issues a DataWordResetN_Rx1 Data Task .
Device reads the Command register and notes task types
Device carries out the Data task by copying the first N data
words of the data buffer into the Read Data registers.
The above 3 steps can be repeated (Using DataWordN
tasks) to read many words out of the device.
1
1
1
1
0
0
3
4
1
1
1
1
0
1
0
0
5
6
7
0
1
1
1
0
1
1
1
1
0
0
0
8
7.7.5 Rx Tasks
AbortRx1/Rx2
This causes the current task on the specified Rx channel to abort. It also clears the modem buffer
of the specified Rx channel.
RxB1/2: Receive Burst on Rx1/Rx2
This causes the specified Rx channel to wait for a good training sequence and start flag, then
demodulate, decode and store the burst in its data buffer. See section 7.7.1 for a detailed
discussion of AIS burst reception. The recovered data can be read by the host issuing an
appropriate Data Task. The first four words of the buffer contain the burst information:
Word1 ($A9) – Burst length in bytes.
Word2 ($AA) – Value proportional to DC offset of Rx Input.
Word3 ($B8) – Time of arrival, measured in 24kHz ticks from the SLOTCLK.
Word4 ($B9) – Slot Counter at Time of Arrival
Note: RXB1/2 tasks can only be issued when the Rx Raw bit is cleared to 0.
RxR1/2: Receive N Raw words on Rx1/Rx2
This causes the specified Rx channel to wait for a good training sequence and start flag, then
demodulate and store N words in its Data buffer. N is specified in the Rx data count register. Burst
information is NOT recorded in Raw mode, so there are an additional 4 words available in the
Data Buffer compared with Burst mode operation.
Note: RxR tasks can only be issued when the Rx Raw mode bit is set to 1.
2012 CML Microsystems Plc
42
D/7032/42_FI1.2/13
CMLMICRO [ CML MICROCIRCUITS ]
