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Internal frequency

discriminating signals

Signal discriminated

at A3OP terminal

RXDT- terminal

output signals

DATA VALID

DATA VALID

A3OP terminal signal

RXCK terminal output

DATA VALID

RXDT- terminal output

15

16

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

1

2

3

One bit data group (16 waves)

4 waves

4 waves

8 waves

Function and Operation

As the normal frequency of the internal master clock is 17.1776 MHz, one clock count is equivalent to

130.133... kHz (17.1776 MHz divided by 132 = 130.133... kHz). Accordingly, a signal is identified as bit

data “1” with the resulting negative level output at the “RXDT–“ terminal when the signal frequency at the

“A3OP” terminal is 130.133... kHz or less, and it is identified as bit data “0” with the resulting positive level

output at the “RXDT–“ terminal when the signal frequency at the “A3OP” terminal is over 130.133... kHz.

An additional feature is included to maximize the stability of the above-mentioned FSK signal

demodulating system based on binary notation: the system incorporates a circuit which disables definition

of an “RXDT–“ signal unless more than four consecutive FS-keyed signal waves are identified within the

same frequency band during binary discrimination. This protects the once defined “RXDT–“ signal in the

bit data form from being affected by sporadic events. For instance, even when its discrimination result is

sporadically inverted due to some noise effects, it is not affected if only three or less consecutive FSkeyed

signal waves are identified at the “A3OP” terminal. (See the diagram below.)

Note: For the timing between “A3OP” and “RXDT–“ signals, refer to the section describing “Input-Output

Specifications”.

The signals demodulated through the above-mentioned process are sequentially output from the “RXDT–“

terminal in bit strings (“1” or “0”). To delimit these continuous bit strings, clock signals are output from the

“RXCK” terminal in synchronization with each bit data.

In normal operating conditions (when data communication can be properly performed between the

RI-RFM-006A and a TIRIS transponder), each bit data group sent from the remote transponder is

composed of sixteen consecutive signal waves belonging to the same frequency band (consisting of two

wave groups, 134.2-kHz high and 123.2-kHz low in terms of normal values). Therefore, clock signals at a

frequency resulting from a simple division of the “A3OP” terminal signal frequency by 16, are output from

the “RXCK” terminal. Then, each “RXCK” clock signal is controlled for output so that its first transition falls

after four consecutive “A3OP” signal waves from the “RXDT–“ signal change point. This enables an

external controller to obtain the relevant bit data without fail provided that each “RXDT–“ signal is fetched

well timed with the first transition of each “RXCK” signal. (See the diagram below.)

8

TIRIS RF-Module IC for Automotive

SCBU036 – December 1996

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