AIS Baseband IC with/without RF Synthesiser
CMX7032/CMX7042
7.6.1 Transmit Tasks
AbortTx:
This causes the current task on the Tx channel to abort. It also clears the Tx modem buffer.
TXB: Transmit AIS Burst
This task can only be executed if the Tx Raw bit (bit 5 in the command register) is cleared to 0.
This causes the CMX7032/CMX7042 to take the contents of the Tx Data buffer, apply AIS data
coding and transmit the resulting AIS message. The transmit sequence will start on the next
SLOTCLK edge.
The following four transmit tasks can only be executed if the Tx Raw bit is set to 1:
TDBS: Transmit Data Buffer on SLOTCLK
This causes the CMX7032/CMX7042 to transmit the data buffer contents using AIS modulation.
No data coding is applied, the Transmit Sequence will start on the next SLOTCLK edge.
TDB: Transmit Data Buffer
This causes the CMX7032/CMX7042 to transmit the data buffer contents using AIS modulation.
No data coding is applied. The data will be transmitted as the modulator is available (Transmit
Sequence is ignored).
PRBS: Transmit pseudorandom bit sequence
This task causes the CMX7032/CMX7042 to transmit an internally generated pseudorandom bit
sequence. The sequence is 511 bits in length, but will repeat indefinitely until aborted using the
AbortTx task, (Transmit Sequence is ignored).
TRW: Transmit Repeated Word
This task causes the CMX7032/CMX7042 to repeatedly transmit the first word currently in the data
buffer. Transmission will start immediately and will continue until an Abort Tx task is issued,
(Transmit Sequence is ignored).
HCT: Hardware Control Task
Allows manual control of ancillary hardware functions.
7.6.2 AIS Burst Mode Transmit
In AIS burst mode, the CMX7032/CMX7042 responds to a TXB task by performing bit stuffing, NRZI
encoding and the addition of training sequence, start/stop flags and CRC checksum as required by AIS.
Note: in AIS burst mode, the data words are automatically transmitted least significant bit first as required
by the AIS specification.
A number of error conditions are checked for during AIS burst mode transmit, each of which causes
transmission to be aborted and a Tx Done interrupt to be generated. The associated Tx states are:
Tx aborted, message too long:
This occurs if the internal message buffer is not big enough for the HDLC coded data (should not
happen in normal operation, as the message buffer is big enough for a 5-slot message). This condition
requires the µC to issue a AbortTx task.
Tx aborted, carrier sensed:
This occurs if the CSTDMA mechanism is enabled and the CS measurement has exceeded the CS
Threshold. The data is retained so that it can be re-transmitted in a subsequent slot (by issuing
another TXB task) should the host request it. The slot selection should follow the rules given in the
relevant international standard.
Tx aborted, buffer not ready:
This occurs in burst mode if the internal data coding has not completed before the timing_start value
expires.
2012 CML Microsystems Plc
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D/7032/42_FI1.2/13
CMLMICRO [ CML MICROCIRCUITS ]
