FX980 datasheet(39/86 Pages) CMLMICRO

39 / 86 page

TETRA Baseband Processor

FX980

D/980/3

LoopBackCtrl

Title:

LoopBack Control register

Address:

$0x0D

Function:

Description:

This register is only used for test purposes. For normal operation all these bits should be

inactive.

Bit

Name

Active State

Function

7:6

Reserved. These bits should be set Low. Undefined on

read.

FirReset

High

When active, this bit holds all FIR filters in reset, by

resetting the FIR address pointers. This by itself does not

reset the data register RAMs. A separate access is

provided to disable the complete Tx or Rx Data path.

Taking N_RESET Low will also reset the FIR filter

coefficients to their default values.

DigLoopBack

High

When set active this bit enables the digital loopback

feature. This connects the output of the Rx Data path

49-tap filter to the input of the Tx Data path 49-tap digital

filter, thereby allowing an analogue signal presented at the

Rx inputs to be filtered by a raised cosine filter and

monitored at the Tx outputs as an analogue signal.

AnaLoopBack

High

When set active this bit enables the analogue loopback

feature. This connects the output of the Tx Data path DAC

to the input of Rx Data path ADC, thus passing transmit

constellation data through a raised cosine filter and allowing

the resultant data samples to be monitored digitally at the

Rx output.

RxDPAccessSel

High

When set active this bit disables the Rx Data path sample

clock, thereby enabling the Data path access register to

directly update the output of the Rx Data path operator.

TxDPAccessSel

High

When set active this bit disables the Tx Data path sample

clock, thereby enabling the Data path access register to

directly update the input to the 15-tap digital filter without

the data being overridden by subsequent sample clocks

TxtoRxDataPath

High

When set active this bit connects the Tx (I,Q) DAC input to

the serial receive port (Rx). This enables the output of the

transmit 15-tap filter to be observed in real time. Data is

taken from the I and Q channels on alternate 144kHz

sample clocks.

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