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Used mainly for the control signal of DPT.
- Cch communications
Communicated by the data (8kbps) converted by the serial/parallel-
converting circuit in ASIC.
Used mainly for recognizing the terminal model.
- PT current-supply circuit
+15V/+40V is superimposed on the transmit/receive data line (D1,
D2), and fed to PT. Supply voltage is +15V for old DPT and APT,
and +40V for new DPT. It will be switched after the connected PT
is judged through communications. I/O control is as follows.
PT_POW
H
H
L
L
For protection against risks such as an overcurrent due to +15V
short in wiring, 300mA constant-current circuit by Q1, Q2, and R25
is used. In case of +40V, 20mA and 80mA constant-current circuits
by Q4, U3, R7, and R27 are used.
The following is the flow chart of telephone switching at boot-up.
8.2.2. SLT interface
- CODEC control......IC251, IC252
Infineon-manufactured PEB2466 is used. The analog
characteristics, such as BN, frequency characteristic, level, and
sidetone, are set by the CODEC interface DCLK, CS, DOUT, and
DIN. The built-in I/O port is used for HOOK detection, DTMF
PT_CUR
H
L
H
L
26
15V
0V
40V80mA
40V20mA
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