FX980 datasheet(12/86 Pages) CMLMICRO

12 / 86 page

TETRA Baseband Processor

FX980

D/980/3

1.5.6.2 Command Read Interface

Command read data is either output on one of the serial read ports, or driven out in the last 8 bits

(data field) on the Cmd port. When command read data is output on a serial read port, the read

address is put in the most significant half of the word, and the read data in the least significant half.

MSB

LSB

Read Address

Data

Command Read Serial Word

1.5.6.3 Rx Data Interface

The Rx Data interface is used only for output of the I and Q received data, unless it is operating in the

mode where CmdRd data is directed to it. When data reception is enabled, I and Q received data will

be output at either 8x or 4x the symbol rate, under control of command register RxSetup2. (see

Section 1.5.7). This is achieved by reducing the serial interface clock rate from MCLK/2 to MCLK/4

and discarding alternate data samples under control of command registers ConfigCtrl1 and

RxSetup2. 16-bit I and Q data words are output at the Rx Data interface, I data and MSB first (by

default), on the rising edge of SClk.

1.5.6.4 Transmission of Data

The address of the Tx FIFO is given consecutive locations ($0x04-$0x07), which allows the address

bits A1 and A0 (bits 11 and 10) of the Command Transmit Data Serial Word to be utilised as transmit

control functions. Data to be transmitted can be in either one or four (2-bit) symbol blocks, which are

subsequently modulated into the DQPSK constellation, or in 3-bit words, which map directly into

constellation points according to the table shown below.

3 bit

code

000

001

010

011

100

101

110

111

0.7071

-0.7071

0.7071

-1

-0.7071

-1

0.7071

-0.7071

Constellation map

The user initiates a transmit frame by asserting the TxEn bit in the TxSetup register.

However,

internal transmission of the data will wait until specific conditions have been met. Firstly, a valid data

word must be written into the FIFO with the TxRampEn bit of the TxSetup register asserted.

Secondly, the internal symbol clock must be active.

Therefore there is a variable delay between

asserting the TxEn bit and transmission starting.

The user may poll the TxPathEn bit of the

TxFIFOStatus register to establish when transmission has started, and in this case the active state of

TxPathEn in High. In general, the user will wish to know when the transmit frame has completed.

This is indicated by TxPathEn returning Low.

To relieve the user of polling overheads when waiting for Tx frame completion, an interrupt can be set

up to occur on the transition of the TxPathEn bit from High to Low.

In such circumstances, the

interrupt activation state of the TxPathEn can be considered Low.

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