GMSK Packet Data Modem and RF Transceiver
CMX990
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 1 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.
TSB - Transmit Single Byte
This task takes a byte from the Data Buffer and transmits the 8 bits, bit 7 first.
Once the modem has read the data byte from the Data Buffer, the BFREE and IRQ bits of the
Status 1 Register will be set to ‘1’, indicating to the µC that it may write the next task and its data
to the modem.
TSO - Transmit Scrambler Output
This task, intended for channel set-up, enables the scrambler and transmits its output.
When the modem has started the task the Status 1 Register bits will not change and hence these
will not raise an IRQ. The µC may write the next task and its data to the modem at any time and
the scrambler output will stop when the new task has produced its first data.
TSD - Transmit Short Data Block
This task takes 4 bytes of data from the Data Buffer, calculates and applies a 16-bit CRC and
forms the FEC for the 4 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 1 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.
RESET - Stop any current action
This task takes effect immediately, and terminates any current task the modem may be
performing and sets the BFREE bit of the Status 1 Register to ‘1’, without setting the IRQ bit. It
should be used when VDD is applied to set the modem into a known state.
Note that due to delays in the internal circuitry, it will take approximately 3 bit times for any
change to become apparent at the transmitter output.
ã 2004 CML Microsystems Plc
27
D/990/1
CMLMICRO [ CML MICROCIRCUITS ]
