Functional Description

Decoder

countries in the world. The signal format, truth table and timing of the decoder are shown below.

The signal format of the call progress tone

Tone

Frequency

Condition

Precision Dial Tone

350Hz + 440Hz

Continuous

Old Dial Tone

120Hz(or 133Hz, ..) + 600Hz

Continuous

Precision Busy Tone

480Hz + 620Hz

0.5sec On and 0.5sec Off

Old Busy Tone

120Hz + 600Hz

0.5sec On and 0.5sec Off

Precision Reorder Tone

480Hz + 620Hz

0.3sec On and 0.2sec Off

Old Reorder Tone

120Hz + 600Hz

0.2sec On and 0.3sec Off or 0.25sec

On and 0.25sec Off

Precision Ring-back Tone

440Hz + 480Hz

2sec On and 4sec Off

Old Ring-back Tone

40Hz (or the others) + 420Hz

2sec On and 4sec Off

The truth table of the decoder

Tone

Transition No.

DIAL

RBK

BUSY

DV

OE/HKOFF

Initial

—

0

0

0

0

0

Dial

1

1

0

0

1

0

Ringback

2~4

0

1

0

1

0

Busy/Reorder

5~16

0

0

1

1

0

Overflow

over 16

0

0

0

1

0

Output Disable

—

Hi-Z

Hi-Z

Hi-Z

*

1

Notes: Hi-Z: Hi impedance

*: previous state

HT9020

7

21st Aug ’98