CMX625P4 CMLMICRO [CML Microcircuits], CMX625P4 Datasheet - Page 19

• Manufacturer Part Number: CMX625P4
• Description: ISDN TA POTS Interface
• Manufacturer: CMLMICRO [CML Microcircuits]

ISDN TA POTS Interface
1.5.13 DTMF Tone Decoder
This block is enabled or disabled by bit 5 of the SETUP Register. If disabled, bit 4 and 5 of the STATUS
Register and bit 0 to bit 3 of the DTMF RX DATA Register are set to ‘0’ and no interrupts are generated.
When bit 5 of the SETUP Register is enabled and bit 4 of the INTERRUPT MASK Register is set to ‘1’ (i.e.
unmasked) a ‘detected tone’ generates an interrupt and bit 4 of the STATUS Register is set to ‘1’.
Reading the STATUS Register clears the IRQN output.
When bit 5 of the SETUP Register is enabled and bit 5 of the INTERRUPT MASK Register is unmasked
(logic ‘1’), a ‘status change’ of the decoder will generate an interrupt and bit 5 of the STATUS Register will
be set to ‘1’. The validity of the data is indicated by bit 4 of the STATUS Register. The decode truth table
is shown below. Reading the STATUS Register clears the IRQN output. An interrupt is not generated
when ‘no tone’ is detected.
A status change of the decoder and the generation of an interrupt (when the INTERRUPT MASK Register
bit 5 is unmasked) will occur both when a tone is first decoded and also when a tone, which was previously
present, is no longer decoded. In the latter case, bit 4 of the STATUS Register will be set to ‘0’ to indicate
that no tone was detected.
The decoded tone pair is indicated by bits 0-3 in the DTMF RX DATA Register.
2001 Consumer Microcircuits Limited
Bit 3
(D3)
DTMF RX DATA Register Bits 0 - 3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
Bit 2
(D2)
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
Bit 1
(D1)
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
Bit 0
(D0)
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Lower Frequency
19
(Hz)
941
697
697
697
770
770
770
852
852
852
941
941
941
697
770
852
DTMF Tone Pairs
Upper Frequency
1633
1209
1336
1477
1209
1336
1477
1209
1336
1477
1336
1209
1477
1633
1633
1633
(Hz)
Keypad
Legend
D
A
B
C
1
2
3
4
5
6
7
8
9
0
#
*
CMX625
D/625/2