Wireless Modem Data Pump
FX909A
RSB - Read Single Byte
This task causes the modem to read the next 8 bits and translate them directly (without de-
interleaving or FEC) to an 8-bit byte which is placed into the Data Buffer (B7 will represent the
earliest bit received). The BFREE and IRQ bits of the Status Register will then be set to '1' to indicate
that the µC may read the data byte from the Data Buffer and write the next task to the Command
Register.
This task is intended for special tests and channel monitoring - perhaps preceded by an SFS task.
LFSB - Load Frame Sync Bytes
This task takes 2 bytes from the Data Buffer and updates the Frame Sync detect bytes. The MSB of
byte '0' is compared to the first bit of a received Frame Sync pattern and the LSB of byte '1' is
compared to the last bit of a received Frame Sync pattern. This task does not enable Frame Sync
detection.
Unlike other Rx tasks, the data buffer must be loaded before the task is issued and the task must
only be issued 'between' received messages, i.e. before the first task for receiving a message and
after the last data is read out of the data buffer.
Once the modem has read the Frame Sync bytes from the Data Buffer, the BFREE and IRQ bits of
the Status Register will be set to '1', indicating to the µC that it may write the next task to the modem.
T7H - Transmit 7-byte Frame Head
This task takes 6 bytes of data from the Data Buffer, calculates and appends 8 bits of FEC from
bytes '4' and '5' then transmits the result as a complete Mobitex Frame Head.
Bytes '0' and '1' form the bit sync pattern, bytes '2' and '3' form the frame sync pattern and bytes '4'
and '5' are the frame head control bytes. Bit 7 of byte '0' of the Data Buffer is sent first, bit 0 of the
FEC byte last.
Once the modem has read the data bytes from the Data Buffer, the BFREE and IRQ bits of the
Status Register will be set to '1', indicating to the µC that it may write the next task and its data to the
modem.
TQB - Transmit 4 Bytes
This task takes 4 bytes of data from the Data Buffer and transmits them, bit 7 first.
Once the modem has read the data bytes from the Data Buffer, the BFREE and IRQ bits of the
Status Register will be set to '1', indicating to the µC that it may write the next task and its data to the
modem.
TDB - Transmit Data Block
This task takes 18 bytes of data from the Data Buffer, calculates and applies a 16-bit CRC and forms
the FEC for the 18 data bytes and the CRC. This data is then interleaved and passed through the
scrambler, if enabled, before being transmitted as a Mobitex Data Block.
Once the modem has read the data bytes from the Data Buffer, the BFREE and IRQ bits of the
Status Register will be set to '1', indicating to the µC that it may write the next task and its data to the
modem.
Note: In transmit mode the CRC checksum circuit is initialised on completion of any task other than
NULL.
ã 1996 Consumer Microcircuits Limited
18
D/909A/4
CMLMICRO [ CML MICROCIRCUITS ]
