AK2305 Datasheet, PDF (19/43 Pages) Asahi Kasei Microsystems – Dual PCM CODEC for ISDN TERMINAL ADAPTER

ASAHI KASEI
DTMF RECEIVER
This circuit detects and decodes the DTMF signal and outputs the 4bits code.
See the following table.
Output code table
Low Tone
[Hz]
697
770
852
941
697
770
852
941
High Tone
[Hz]
1209
1336
1477
1209
1336
1477
1209
1336
1477
1336
1209
1477
1633
1633
1633
1633
KEY
1
2
3
4
5
6
7
8
9
0
*
#
A
B
C
D
DTO
n3
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
DTO
n2
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
DTO
n1
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
(n=0,1)
DTO
n0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
DECODED OUTPUT
Decoded DTMF signals are output at DTO00-03,10-13 pins through tri-state buffers.
The outputs are enabled by DTOE pin.
DTOE
Input
0
DTO00-03, DTO10-13
Output
Hi-Impedance
1
Decoded Output
[AK2305]
GUARD TIME SETTING
Input Signal Available Time(tREC) and Inter Digit Pause Time(tID) can be settled by adjusting Guard Time as
follows. Guard Time is adjusted by GTPn, GTAn(n=0-3.)
Input Signal Available Time(t_REC) = Detecting Signal Time(t_DP)
+ Guard Time(t_GTP)
Inter Digit Pause Time(t_ID)
= Detecting Signal-stop Time(t_DA) + Guard Time(t_GTA)
Range of adjusting Guard Time(t_GTP, t_GTA)
Step of adjusting Guard Time(t_GTP, t_GTA)
1ms - 121 ms
8ms
Regarding the relation between GTPn / GTAn(n=0-3) and Guard Time, see the next page.
Also the relation between Input Signal Available Time(t_REC) and Inter Digit Pause Time(t_ID) is shown.
C0029-E-02
19
1999/8