TDA7540B datasheet(34/75 Pages) STMICROELECTRONICS

34 / 75 page

Functional description

TDA7540B

34/75

This is detected by a control logic and an external search stop output is changing from LOW

to HIGH. The frequency range inside which a successful count result is adjustable by the

EW bits.

tCNT = (CF + 1696+1) / fIF FM mode

tCNT = (CF + 10688+1) / fIF AM up conversion mode

tCNT = (CF + 488+1) / fIF

AM mode

Counter result succeeded:

tTIM ≥ tCNT - tERR

tTIM ≤ tCNT + tERR

Counter result failed:

tTIM > tCNT + tERR

tTIM < tCNT - tERR

tTIM = IF timer cycle time (sampling time)

tCNT = IF counter cycle time

tERR = discrimination window (controlled by the EW registers)

The IF counter is only started by inlock information from the PLL part. It is enabled by

software (IFENA).

Adjustment of the measurement sequence time

The precision of the measurements is adjustable by controlling the discrimination window.

This is adjustable by programming the control registers EW.

The measurement time per cycle is adjustable by setting the registers IFS.

Adjust of the Frequency Value

The center frequency of the discrimination window is adjustable by the control registers CF.

4.5

I2C-Bus interface

The TDA7540 supports the I2C-Bus protocol. This protocol defines any device that sends

data onto the bus as a transmitter, and the receiving device as the receiver. The device that

controls the transfer is a master and device being controlled is the slave. The master will

always initiate data transfer and provide the clock to transmit or receive operations.

4.5.1

Data transition

Data transition on the SDA line must only occur when the clock SCL is LOW. SDA transitions

while SCL is HIGH will be interpreted as START or STOP condition.

4.5.2

Start condition

A start condition is defined by a HIGH to LOW transition of the SDA line while SCL is at a

stable HIGH level. This "START" condition must precede any command and initiate a data

transfer onto the bus. The device continuously monitors the SDA and SCL lines for a valid

START and will not response to any command if this condition has not been met.

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