TETRA Baseband Processor
FX980
1.5.4.3 Power Ramping and Control
One of the DACs has an additional feature which enables a set of values to be sequenced out at a
pre-selected frequency. This is aimed at enabling power ramping of a RF output with a suitable profile.
The sequence may be reversed for power down. The sequence of values is stored in a dedicated
RAM, which can be loaded via the serial interface.
1.5.5 IRQ Function
An interrupt request (IRQ) pin is provided for asynchronous communication with an external
processor. The IRQ (asserted low) will be asserted when any of the error or user information flags are
activated by an internal operation. Some examples of operations which may generate an IRQ are:
1. An attempt by the user to write to a full Tx data-input FIFO
2. An attempt is made by the Tx to read from the Tx data-input FIFO when it is empty.
3. An internal arithmetic overflow has occurred in an FIR filter.
The IRQ feature may also be used to establish the phasing of the received I and Q channel data from
the RxDat serial port should synchronisation be lost for any reason.
The cause of the IRQ can be obtained by reading the error flags register. All possible causes of an
IRQ are masked on reset. Mask status can be altered by writing to the IRQ mask register.
Note that default coefficients and settings have been optimised to maximise performance and should
not cause arithmetic overflows. However, use of non-default coefficients, large offset corrections or
large Tx phase adjustments may cause problems, which can be corrected by scaling down coefficients
or via the gain multiplier feature.
1.5.6 Serial Interface
All digital data I/O and control functions for the FX980 are via the serial interface. It is expected that
the FX980 will be used in conjunction with a DSP and/or other processor. The device has three serial
interface ports, each port is based on the industrial standard three wire serial interface. This interface
allows communication with standard DSP ICs using a minimum of external components. The three
serial interface ports are:
Cmd
Command port, generally this is an input port receiving commands and data from the host,
but may also be configured as a bi-directional I/O interface.
CmdRd
RxData
Command read port, an output port to send command read data back to the host. Read
data is only sent on this port in response to a read command.
Receive data port, an output port to send receive data back to the host. Data is only
present on this interface when the Rx Data path is active. This port may also be
configured as the CmdRd port.
ã 1997 Consumer Microcircuits Limited
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D/980/3
CMLMICRO [ CML MICROCIRCUITS ]
