em78p811 ELAN Microelectronics Corp, em78p811 Datasheet - Page 26

• Manufacturer Part Number: em78p811
• Description: 8-bit Micro-controller
• Manufacturer: ELAN Microelectronics Corp

VII.9.3 Ring detect circuit
resistor network R2 to R3 attenuates the incoming power ring applied to the top of R2. The values given have been
chosen to provide a sufficient voltage at DET1 pin, to turn on the Schmitt trigger input. When Vt+ of the Schmitt is
exceeded, cap C1 will discharge.
between the individual cycle of the power ring. With /RINGTIME enabled, this signal will be a /RD signal in RA
throught a buffer.
VII.10 DTMF ( Dual Tone Multi Frequency ) Tone Generator
of DTMF tone . One is the group of row frequency, the other is the group of column frequency, each group has 4 kinds of
frequency , user can get 16 kinds of DTMF frequency totally. DTMF generator contains a row frequency sine wave
generator for generating the DTMF signal which selected by low order 4 bits of RB and a column frequency sine wave
generator for generating the DTMF signal which selected by high order 4 bits of RB. This block can generate single tone
by filling one bit zero to this register.
effective value, tone output will be disable. Recommend value refer to table as follow please :
_________________________________________________________________________________________________________________________________________________________________
* This specification is subject to be changed without notice.
Det1
Vdd
When Vdd is applied to the circuit, the RC network will charge cap C1 to Vdd holding /RING TIME off . The
The value of R1 and C1 must be chosen to hold the /RING TIME pin voltage below the Vt+ of the Schmitt
If all the values are high , the power of DTMF will turn off until one or two low values.
Either high or low 4 bits must be set by an effective value, otherwise, if any ineffective value or both 4 bits are load
Built-in DTMF generator can generate dialing tone signals for telephone of dialing tone type. There are two kinds
/Ring Time
R2
R1
C1
R3
Fig16. ring detect circuit
25
/Ring Time
/RD
8-bit OTP Micro-controller
EM78P811